The move Thursday came on an off day for the Rangers before 10 consecutive road games. Gentry was on the list for two weeks, and played five rehabilitation games for Triple-A Round Rock.
Right-hander Darren O'Day was optioned to Round Rock to make room on the active roster.
Gentry last played July 24, when his helmet came off as his slid headfirst into second base. His neck twisted when he made contact with the leg of Toronto second baseman Aaron Hill.
Gentry is hitting .265 in 39 games, 24 as a starter.
O'Day was called up Saturday when Alexi Ogando went on the paternity leave list.