The Yankees' closer threw about 20 pitches on Saturday morning in the bullpen at Rogers Centre and reported "no problems at all" with his tight left groin, which has kept him sidelined since a save on Tuesday at Baltimore.
"I wasn't expecting to feel anything," Rivera said. "I just have to make sure that it's ready. I wasn't looking for something."
The Yankees have proceeded cautiously regarding Rivera, who has converted a career-high 34 consecutive save opportunities and wields an impressive 1.78 ERA in 55 appearances spanning 55 2/3 innings this season.
Rivera has been battling the recurring tightness since an Aug. 15 appearance at Seattle, but has received treatment regularly to help it subside. Had it been October and not early September, Rivera said he would have been available.
As it is, Rivera could be ready to close for the Yankees in Sunday's series finale and at least one of the games in Monday's day-night twin bill against the Rays in New York.
The Yankees did move to add an extra bullpen arm before Saturday's contest, expressing concern that Chad Gaudin and Joba Chamberlain both went short in the first two games against the Blue Jays and needed relievers to soak up innings.
Veteran right-hander Josh Towers was promoted from Triple-A Scranton/Wilkes-Barre, where he was 7-6 with a 3.05 ERA in 20 games (18 starts) for the International League North Division champions.
Yankees manager Joe Girardi said that Towers, who spent one day on New York's roster in August, but did not pitch, was originally going to be promoted on Monday. With no Rivera, Alfredo Aceves or Mark Melancon available on Saturday, general manager Brian Cashman thought it would be better to add protection.
"[Towers] can give us some distance if we need it, or if we need an inning, he can give us an inning," Girardi said.
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.