Luckily for the Yankees, they do not believe that the matter will be serious for their Hall of Fame closer. Rivera has been battling recurring tightness in his left groin but expects that a few days of rest will allow him to return to duty.
"We're going day by day," Rivera said. "Hopefully, [I can pitch] as soon as possible."
The 39-year-old Rivera, who pitched in the first two games of the Yankees' series against the Orioles, said that the tightness bothered him during Tuesday's 21-pitch appearance.
Rivera originally felt the tightness on Aug. 15, at Seattle, but it dissipated after he received rest. Manager Joe Girardi has his fingers crossed for the same results in September.
"It's a concern for you to run him out there," Girardi said. "We don't want to hurt him. We'll probably give him a few days off and see if we can nip it."
Rivera has converted a career-high 34 straight save opportunities, the longest stretch in the Majors, and has allowed just one earned run over his past 29 appearances. He has a 1.78 ERA and 38 saves in 55 appearances this season.
He has been receiving treatment since the series at Seattle, and says it is better that the tightness is in the left groin, because it does not bother him as much when he pushes off the mound.
"Especially in your legs, you don't want to have those kinds of injuries," he said. "We will take care of it and work at it."
With Rivera out for a few days, Girardi said that he will mix and match in the closer role. Phil Hughes recorded a four-out save on Wednesday in the club's 10-2 victory over Baltimore, and Girardi did not discount the idea that he might see similar action again.
Rivera said that if it were the postseason instead of the first week of September, he would be pitching.
"Oh, definitely," he said. "We have a lot of time, so I don't want to push it and make it worse. We have time."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.