An injured player cannot be outrighted to the minors during the MLB regular season, but most injured players can be outrighted to the minors at certain times during the off-season:
1. An injured player who has accrued less than three years of MLB Service Time in his career and who did not accrue any MLB Service Time the previous season, has not previously been outrighted to the minors, and who was not selected in the immediately-preceding Rule 5 Draft, can be outrighted to the minors during a period of time beginning on the day after the conclusion of the MLB regular season up until the 15th day prior to the start of the next MLB regular season.
CAN BE OUTRIGHTED UNTIL 15TH DAY PRIOR TO 2015 MLB OPENING DAY EVEN IF INJURED (last updated 3-17-2014):
2. Most other injured players can be outrighted to the minors only during a period of time beginning on the day after the conclusion of the MLB regular season up until reserve lists are filed in November, but an injured "Rule 5 Player" can be outrighted during this period only after Rule 5 restrictions have been removed, and a "Draft-Excluded Player" can be outrighted during this period only if Outright Assignment Waivers are requested by 2 PM (Eastern) on the 4th day following the conclusion of the World Series.