"I really couldn't throw it," Posada said. "It just kept locking up, like back spasms, and it kept getting worse and worse as the game went along."
Posada, who was replaced by Kelly Stinnett, is questionable for Saturday's game. General manager Brian Cashman said that the team would not bring a third catcher from the Minors for Saturday.
"This could be gone tomorrow," said manager Joe Torre. "He started gradually tightening up, spasming in his back. He said it felt a little better after the game, but we'll have to wait and see tomorrow. If he's all right, he'll play. If we have to take him out, we'll take him out."
Williams felt his injury in the first inning after doubling in the Yankees' fourth run. Torre and team trainer Gene Monahan visited Williams on the field to check his status, but he remained in the game.
"He feels a little tight muscle in the rump," Torre said. "I hope he doesn't get mad at me for telling you that."
Torre said before the game that he was considering resting Williams on Saturday, and the latest incident clinched that decision.
Farnsworth threw a perfect eighth inning, but when Torre decided to send him back out for the ninth, he told the manager about some tightness in his back. Farnsworth said that the problem is something he experienced throughout the 2005 season, and although he said he would be able to pitch on Saturday, Torre called it "doubtful" that he would do so.
Sheff to start it up: Gary Sheffield was examined by hand specialist Dr. Charles Melone on Friday, and the doctor cleared him for progressive rehabilitation.
Sheffield then picked up a bat for the first time since going on the disabled list with a bruised left wrist on May 6. Sheffield did some work off a tee to test out the wrist. Torre said that the outfielder could take batting practice as early as Saturday.
"Once he takes enough BP and wants to test it, we'll do that," said Torre, who suggested to Sheffield that he play in a rehab game or two when he feels up to it. "I talked to him about it, because there are so many unpredictables that go on in a game that you can't do in batting practice."
Assuming Sheffield has no setbacks, he could return from the DL during the Kansas City series May 26-28, or in Detroit to start the following road trip.
Bubba to the bench: The Yankees placed Bubba Crosby on the 15-day disabled list on Friday, purchasing the contract of outfielder Mitch Jones from Triple-A Columbus and adding him to the roster for Friday's game against the Mets.
Crosby suffered a strain of his right hamstring while diving for a ball in the fifth inning on Thursday night. Although the injury isn't believed to be serious, the Yankees decided to make the move before playing three games under National League rules at Shea Stadium.
"They didn't really have time to wait and see how long it was going to take," Crosby said. "Even if it's six days, they don't have the time to let the team go without a 25th man on the bench, especially with three of these games being in a National League park."
"We don't necessarily think it needs to be 15 days, but knowing we're under the gun here, playing short, we felt it was necessary to DL him because he'd probably have been gone for a week," Torre said. "We didn't think we could afford to be without a player that long."
The Yankees considered bringing up Kevin Thompson, who is having a good season for Columbus, but the outfielder recently suffered a slight hamstring injury of his own, so the Yankees turned to Jones.
Jones, 28, was batting .239 with six home runs and 20 RBIs in 39 games with Columbus in 2006. As a non-roster invitee to Spring Training this year, he batted .304 with four home runs and seven RBIs in 17 games for New York.
"He had a good spring for us and hit some home runs," Torre said. "We didn't see a whole lot of him in the outfield, but he'll play off the bench."
Crosby is expected to return from the DL when he becomes eligible on June 3.
"The way that I play, they don't want to send me out there with a 95 percent hamstring," Crosby said. "They want to make sure it's 100 percent so that, when I do step back on the field, I can play the way they're used to me playing."
Mix and match: The Yankees started Williams in left field, Johnny Damon in center and Melky Cabrera in right on Friday night, marking the 14th different combination the team has used this season (using six players) for its starting outfield.
The Yankees also signed veteran Terrence Long this week, sending him to Columbus. Long, who has played for the Mets, A's, Padres and Royals in a seven-year big-league career, went 1-for-4 in his Clippers debut on Thursday.
Combination No. 15 will likely hit the field on Saturday, as Torre suggested that Kevin Reese would start in left field next to Damon and Cabrera.
Coming up: The Yankees and Mets play the second game of this weekend's Subway Series on Saturday, as Mike Mussina takes on Pedro Martinez in the ninth career meeting between the two right-handers. First pitch is scheduled for 1:20 p.m. ET.