1. Before a player on Optional Assignment can be traded, he must be recalled from his minor league assignment ("Recalled - Not to Report").

2. If a player is claimed off waivers after the conclusion of all of the claiming club's minor league affiliates' seasons, the player can be "Recalled - Not to Report," and the player does not accrue MLB Service Time.

3. All players on Optional Assignment to the minors must be "Recalled - Not to Report" on the day after the conclusion of the MLB regular season. 

Most players get only three minor league options, but a player who has accrued less than five "full seasons" is eligible for a 4th minor league option.

For the purpose of determining eligibility for a 4th minor league option, a player accrues a "full season" when he spends at least 90 days on the Active List and/or Development List of an MLB and/or minor league club or clubs in a given season, or (in seasons prior to 2012) spends at least 60 days but less than 90 days on the Active List of an MLB and/or minor league club or clubs followed by an Injured List assignment where the combined time spent on the Active List and the Injured List equals at least 90 days or (beginning with the 2012 season) spends at least 30 days but less than 90 days on the Active List and/or Development List of an MLB and/or minor league club or clubs followed by an Injured List assignment where the combined time spent on the Active List and the Injured List equals at least 90 days.   
NOTE: Days spent on Optional Assignment to a club's Spring Training Complex in September count as active days toward determining eligibility for a 4th minor league option. 
CoViD-19 EXCEPTION: With regard to a player's eligibility for a 4th minor league option year in 2021 (and beyond), days spent on Optional Assignment in 2020 counted for nothing, and days spent on an MLB Active List and MLB inactive lists (IL, FMLA/Bereavement, Paternity Leave, et al) counted and were calculated at the prorated 2020 MLB Service Time rate (one day equals 2.78 days of MLB Service Time).

If a player qualifies for a 4th minor league option year, the 4th option is available during Spring Training and for the entire MLB regular season. 

CUBS ELIGIBLE FOR 4TH MINOR LEAGUE OPTION: (updated 11-14-2023)
Kevin Alcantara, OF (in 2026 - see NOTE)
Alexander Canario, OF (in 2024 - see NOTE)
Caleb Kilian, RHP (in 2025 - see NOTE) 
Christopher Morel, INF (in 2024 - see NOTE)
NOTE:  Canario and C. Morel will be eligible for a fourth minor league option in 2024, Kilian will be eligible for a fourth minor league option in 2025 if the third option is spent in 2024, and K. Alcantara will be eligible for a fourth minor league option in 2026 if the third option is spent in 2025.   

GENERAL RESTRICTIONS:

1. Beginning with the 2020 season, no more than 14 players (formerly no more than 16 players) on a club's MLB Reserve List (40-man roster) may be on Optional Assignment at any one time prior to September 1st, and no more than twelve players may be on Optional Assignment at any one time beginning on September 1st and extending through the conclusion of the MLB regular season.

2. No player may be optioned to the minors prior to the start of Spring Training.

3. Beginning in 2022, a player can be optioned a maximum of five times in a given season. If a player has been optioned to the minors five times in a given season, Outright Assignment Waivers must be secured before he can be sent to the minors again.   
EXCEPTIONS: If a player has been optioned five times previously in the season and then is claimed off waivers by another club, the claiming club can option the player to the minors one more time as long as the player was not on the claiming club's MLB Reserve List (40-man roster) sometime earlier that season.  
NOTE: Because of the delay of the start of the 2022 MLB regular season, an optional assignment prior to May 2nd did not count toward the five option maximum limit in 2022.

4. Generally an injured player cannot be optioned to the minors. However, an injured player who did not accrue any MLB Service Time during the previous season, has not accrued at least three years of MLB Service Time, and was not selected in the previous Rule 5 Draft, can be optioned to the minors during a period of time beginning on the first day of Spring Training until the 15th day prior to the start of the next MLB regular season. 

CAN BE OPTIONED IF INJURED UNTIL 15TH DAY PRIOR TO 2024 MLB OPENING DAY (last updated 10-2-2023):
Kevin Alcantara, OF
Michael Arias, RHP (Draft-Excluded Player) 
Ben Brown, RHP 
Brennen Davis, OF 
Porter Hodge, RHP (Draft-Excluded Player) 
Bailey Horn, LHP (Draft-Excluded Player) 
Luis Vazquez, INF (Draft-Excluded Player)

5. A player who is optioned to the minors generally must remain on Optional Assignment for at least ten days (for a "position player") or 15 days (for a "pitcher or for a "two-way player"), and a "position-player" optioned to the minors during Spring Training generally must remain on Optional Assignment for the first ten days of the MLB regular season and a "pitcher" or a "two-way player" optioned to the minors during Spring Training generally must remain on Optional Assignment for the first 15 days of the MLB regular season.
EXCEPTIONS: The player is traded or claimed off waivers, is recalled as the extra man for a doubleheader (second game of the doubleheader only if two games were scheduled after a postponed or suspended game from the previous day) or other circumstances, is recalled to replace a player on the MLB Active List (26-man roster) who is traded, claimed off waivers, or placed on the MLB Injured List, Bereavement/Family Medical Emergency List, Paternity Leave List, or Restricted List (but only pursuant to a suspension or administrative leave resulting from a violation or possible violation of the joint MLB-MLBPA JDV policy or a suspension resulting from a violation of the joint MLB-MLBPA JDPTP policy), or is recalled and then optioned back to the minors prior to a game being played where the game is postponed or cancelled. 
NOTE: If a player is acquired in a trade and is optioned to the minors by his new club within 24 hours, the player can be recalled from the Optional Assignment at any time without restriction, but if a player on Optional Assignment to the minors is claimed off waivers and is then optioned to the minors by his new club, the ten-day limit (for "position players") or 15 day limit (for "pitchers" and for "two-way players") does apply. So as far as the ten-day ot 15-day limits are concerned, there is a distinction made between acquiring a player in a trade and claiming a player off waivers. 

6. A player can be optioned to any of his club's minor league affiliates whose season (including post-season) is still in progress as long as the player has not exceeded the maximum number of professional seasons allowed for players at that level, but if the regular season (and post-season) of all four of the MLB club's full-season minor league affiliates have concluded, a player may be optioned to the club's Spring Training Complex in September.   
NOTE: If a player is optioned to his club's Spring Training Complex in September because all of his club's minor league affiliates have concluded their regular seasons and post-seasons, the player will accrue MLB Service Time while on Optional Assignment. A player will also accrue MLB Service Time while on Optional Assignment if he is optioned to any minor league affiliate during the period of time beginning on the Friday after Labor Day extending through the conclusion of the MLB regular season.  

7. A player on Optional Assignment to the minors must be recalled no later than the day after the conclusion of his club's MLB regular season.

OTHER RESTRICTIONS:

8. A Rule 5 "Selected Player" cannot be optioned to the minors until restrictions have been removed.

RULE 5 SELECTED PLAYERS WITH MINOR LEAGUE OPTIONS REMAINING (updated 3-12-2021):
NONE   

9. Beginning on the day after the conclusion of the MLB regular season, a Rule 5 "Draft-Excluded Player" cannot be optioned to the minors any earlier than 20 days prior to MLB Opening Day.
NOTE: An injured player with Draft Excluded Status who otherwise would be eligible to be optioned up until the 15th day prior to MLB Opening Day can be optioned only during a five-day window starting on the 20th day prior to the start of the MLB regular season up until the 15th day prior to the start of the MLB regular season.

DRAFT-EXCLUDED PLAYER WITH MINOR LEAGUE OPTIONS REMAINING (last updated 11-14-2023):
Michael Arias, RHP (see NOTE) 
Porter Hodge, RHP (see NOTE)  
Bailey Horn, LHP (see NOTE) 
Luke Little, LHP 
Luis Vazquez, INF (see NOTE) 
NOTE: Once Draft-Excluded Player status is removed, player can be optioned to minors even if he is injured up until 15th day prior to start of 2024 MLB regular season. 

10. Per Article XIX-A of the CBA, any player on an MLB 40-man roster who has accrued at least five years of MLB Service Time (as well as an international player with Article XIX-A contractual rights) has the right to refuse an Optional Assignment to the minors, or the player can elect to be a free-agent immediately upon being optioned (he has two days to decide).
NOTE: If a player with Article XIX-A rights refuses an Optional Assignment but does not elect free-agency, the club must either retain the player on the club's MLB Reserve List (40-man roster) AND Active List, trade the player, or give the player his Outright Release.

11. A player with Article XIX-A rights can waive his right to refuse an Optional Assignment in advance, but the waiver cannot be signed more than ten days prior to MLB Opening Day, the player has the right to designate in advance which minor league team to which he can be assigned, and the waiver automatically expires if the player is not optioned to the minors within 45 days or by the 45th day of the MLB regular season (whichever is later).

CUBS ARTICLE XIX-A PLAYERS WITH MINOR LEAGUE OPTIONS REMAINING (last updated 11-4-2023): 
Yan Gomes, C 
Ian Happ, OF 
Kyle Hendricks, RHP
Drew Smyly, LHP 
Seiya Suzuki, OF (International player with Article XIX-A rights)
Dansby Swanson, INF 
Jameson Taillon, RHP