To be playoff eligible you must be one of the following on August 31st:
- on the 25 man major league roster, or
- on the disabled list (7, 15, or 60 day DL), or
- on the suspended list, or
- on bereavement leave, or
- on military active duty
In addition, a club can replace any player who is injured at the time that playoff rosters are submitted. So, for every injured player, the club can add a player who was not on the major league roster, or any of the above eligibility lists at the end of August. In order to be eligible to be added in place of an injured player, one need not be on the 25 man roster, nor even the 40 man roster as of August 31. Any player in the organization as of August 31 can be used to replace an injured player, with permission from the commissioner’s office.