1. No player may be optioned to the minors prior to the start of Spring Training.
2. An injured player cannot be optioned to the minors.
3. A player who is optioned to the minors generally must remain on Optional Assignment for at least ten days. (A player optioned to the minors during Spring Training generally must remain on Optional Assignment for the first ten days of the MLB regular season). The only exceptions are if the player is recalled as the "26th man" for a day where a doubleheader was scheduled at least 48 hours in advance (or for the second game of the doubleheader only if the doubleheader was scheduled less than 48 hours in advance), or is recalled to replace a player on the 25-man roster who is placed on an MLB inactive list (Disabled List, Bereavement List, Paternity List, Restricted List, et al), or if the season (including post-season playoffs) of the minor league team to which the player is assigned is over, or if the player is traded.
4. All players on Optional Assignment to the minors must be recalled no later than the day after the conclusion of the MLB regular season.
5. A "Rule 5 Player" cannot be optioned to the minors until Rule 5 restrictions have been removed.
RULE 5 PLAYERS WITH MINOR LEAGUE OPTIONS REMAINING ON CUBS 40-MAN ROSTER
6. Beginning on the day after the conclusion of the MLB regular season, a "Draft-Excluded Player" cannot be optioned to the minors any earlier than 20 days prior to MLB Opening Day.
DRAFT-EXCLUDED PLAYERS WITH MINOR LEAGUE OPTIONS REMAINING ON CUBS 40-MAN ROSTER (updated 8-19-2016)
Felix Pena, RHP
Rob Zastryzny, LHP
7. 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.
If a player eligible to elect free-agency is optioned and elects to be a free-agent immediately, his contract is terminated and he receives no termination pay.
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 (25-man roster), trade the player, or give the player his unconditional release.
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 8-3-2016):
Jake Arrieta, RHP
Trevor Cahill, RHP
Chris Coghlan, OF
Dexter Fowler, OF
Jason Heyward, OF
Munenori Kawasaki, INF (see NOTE below)
John Lackey, RHP
Jon Lester, LHP
Miguel Montero, C
Joe Smith, RHP
Ben Zobrist, IF-OF
NOTE: Kawasaki may or may not have Article XIX-A contractural rights (TBD)