Townsend, out since July 13 with a recurring hamstring injury, tried to run this week but felt more soreness in that hamstring and now will remain on the disabled list.
Townsend is headed to Sarasota to continue his rehab.
When he has played this year, he has hit quite well. In 64 games with the Keys, Townsend was batting .318 with 23 doubles, 13 homers, 50 RBIs and an OPS of .943.
But Townsend has had hamstring issues now for much of the last two seasons. It's possible now that he won't make it back in time to play again this year.
Had Townsend been activated on Sunday, the Orioles were considering moving Aaron Baker, the player they got from the Pirates in the Derrek Lee trade, to Double-A Bowie. For now, Baker will stay with Frederick.
Trent Mummey, who has been out since June 8 with a hamstring injury, could return to the Keys in about a week.