Here is the Cubs 2019 post-season roster eligibility list:
POST-SEASON ROSTER ELIGIBILITY RULES
A club's Post-Season Eligibility List is established at midnight (Eastern) on August 31st.
A club's Active List (25-man roster) must be submitted to the MLB Commissioner prior to the start of the first game of each post-season series (Wild Card game, LDS, LCS, and World Series).
A club's Active List can be changed (tweaked) prior to the start of the first game of each series (WC, LDS, LCS, and WS).
1. A player who received a suspension for violation of the MLB-MLBPA Joint Drug Prevention and Treatment Program (player tested positive for a prohibited substance) prior to the start of Spring Training, during Spring Training, during the regular season, or during a post-season series (Wild Card, LDS, LCS, or World Series), is ineligible to play in any MLB or minor league post-season game(s) or series in that season, even if the player has completed serving the suspension.