"The way he's walking around now, I don't think this thing is just going to change overnight," Joe Torre said. "I hope I'm wrong, but he's pretty uncomfortable right now."
Rivera's absence was felt in a major way on Thursday night, as Kyle Farnsworth blew a save opportunity in the ninth inning, costing the Yankees a potential win against the Tigers.
"Having Mo, he's such a lethal weapon for us," Alex Rodriguez said. "But no matter who is out, we have enough to win. That's not an excuse to lose games."
"It seems he does it so effortlessly, but we know it's not," Torre said of Rivera. "Mo is like an everyday player for us."
Rivera was treated and evaluated during batting practice and into the early innings of the game. He was seen by a chiropractor, who gave him some muscle relaxers to loosen up the back.
"It hurts right now; it hurts more because we lost the game," Rivera said. "It's tough. That's my job, so to sit like this is horrible. Hopefully tomorrow is a better day.
"I couldn't believe something like that could happen putting on my shoes," he added. "I'm not a doctor. We'll see how I feel tomorrow and we'll go from there."
The Yankees currently have seven players on the disabled list, as Gary Sheffield was placed on the DL earlier in the day.
In addition to those players, Johnny Damon, Derek Jeter and Jorge Posada have each been nursing injuries.
"It's laughable at this point," Torre said. "Obviously, you don't make light of anything, but every day it's something different. What are you going to do?"
Jeter still out: Jeter was out of the lineup for the second consecutive day, as Torre decided to give the shortstop and his sore right hand another day to heal.
Jeter suffered the injury on Monday night, though he was back in the lineup on Tuesday. After watching Jeter go 0-for-5, Torre decided to rest him on Wednesday and Thursday.
"He was all right to play, and if I need to use him, I'll use him," Torre said. "Knowing how much he was favoring it the other night, he's been in such a good groove, I don't want to get him out of that."
Jeter, who hates missing games for any reason, seemed bothered that he wasn't in the lineup, but he said that whatever decisions Torre makes, he will respect them.
"I don't like to sit out," Jeter said. "Am I bothered by Mr. T? No, I understand where it's coming from."
"I always feel it bothers him more than he says it bothers him," Torre said. "That's a given."
Torre said that chances were "real good" that Jeter would play on Friday, but Jeter went one step farther.
"I'm playing tomorrow," Jeter said. "You can write it in pen."
Johnny's back: Damon returned to the lineup after missing two games to rest the broken sesamoid bone in his right foot. The center fielder believed that the two days off helped him tremendously, as his foot felt considerably better.
"It's where I need to be right now," Damon said. "I'm not feeling any discomfort, so hopefully that doesn't change."
Team trainer Gene Monahan taped Damon's big toe to his second toe, trying to keep the big toe from bending as much as usual. Damon may still go for more tests on his foot this week in New York, though he said that even if he doesn't get tests, he will see a foot specialist.
"I'm happy that the team was able to withstand me not playing for a couple of days and we emerged victorious," Damon said. "It says a lot about the players we have."
Waiting on Bubba: Bubba Crosby, on the DL with a strained right hamstring, won't begin playing in extended Spring Training games until the middle of next week.
"He still feels it," Torre said. "I don't want to say he's gone backwards, he just hasn't progressed as we had hoped. It's going to be a little while."
Crosby could return to the Yankees by next weekend's series at home against Oakland.
Trenton-bound: Shawn Chacon threw a bullpen session before Thursday's game, and assuming he has no setbacks on Friday or Saturday, he will pitch a rehab game for Double-A Trenton on Sunday.
Chacon, on the DL with a hematoma on his left leg, could return to the Yankees' rotation after that start, though a second rehab outing is a possibility.
"We're hopeful it will be just one," Torre said.
New arrival: Kevin Thompson joined the Yankees on Thursday, taking Sheffield's spot on the roster after the outfielder was placed on the DL.
Thompson, 26, hit .288 with five home runs and 13 RBIs in 36 games with Triple-A Columbus this season. He missed about 10 days earlier this month with a right hamstring injury, but he said that problem was behind him.
Thompson will play off the bench for the Yankees, while Terrence Long and Bernie Williams will share time in right field in Sheffield's absence.
"I'm happy to be here. I'm just hoping to get a chance," Thompson said. "You always want to be here, but this is just a step, so you can't be satisfied. You have to take the next step."
Coming up: The Yankees make their first trip of the season to Baltimore, opening a three-game set against the Orioles on Friday. Jaret Wright takes on Kris Benson, with first pitch scheduled for 7:05 p.m. ET.