Rivera said his back started nagging him between the shoulder blades after he took the loss in Friday night's 1-0 defeat against the Angels.
The All-Star closer said it was nothing to be concerned about, but it was uncertain whether he'd be available to pitch Monday night at Texas in the opener of a 10-game trip.
While the Yankees hit the road, Hideki Matsui is headed to Florida for rehabilitation on his swollen left knee.
Hoping to avoid season-ending surgery, Matsui was scheduled to go to the team's complex in Tampa, Fla., on Monday to continue his rehab program. Wearing a new brace, the designated hitter and part-time left fielder has been hitting off a tee and riding an exercise bike.
"So far the brace has worked," Girardi said. "Obviously, the activity he's had isn't really baseball activity."
The Yankees still don't know if Matsui will be able to return this season.
"You just take it day by day. You see how he responds each day," Girardi said. "You just try to build him up."
In other injury news, Robinson Cano didn't start for the second consecutive game because of a sore left hand, but he came off the bench for defense in the eighth inning and later delivered a two-run single.
Pavano started and allowed one run and five hits in three innings. Hughes yielded one hit and struck out five in 3 2/3 scoreless innings.
"I'm encouraged by the numbers," Girardi said.