Rainey was optioned to Triple-A Rochester on Sunday, Mark Zuckerman of MASNSports.com reports.
Rainey was activated off the 10-day injured list Thursday after recovering from a stress reaction in his lower leg, and he'll head to the minors after giving up a run on two hits and a walk while recording only one out Thursday against the Phillies. The right-hander has a 7.20 ERA, 1.76 WHIP and 31:21 K:BB across 25 innings for the season. According to Zuckerman, Rainey is expected to pitch on a strict every-other-day schedule at Triple-A in an attempt to get him back on track.