Fourth Minor League Option

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.