Posada was placed on the 15-day disabled list Tuesday with a strained right hamstring that is expected to sideline the All-Star catcher for two to three weeks.
It was a frustrating blow to the Yankees and Posada, who toiled through months of a strenuous rehab program to get ready for this season. He missed most of last year due to a right shoulder injury that required surgery.
"This is tough on me because I worked really hard to be here," Posada said. "Just one of those things that you can't control, and you try to stay positive. But it's not easy."
The five-time All-Star was injured while sliding into second base during Monday night's 6-4 loss against the Boston Red Sox. He tweaked the same hamstring earlier in the season, missing a couple of late April starts in Detroit, but avoided the DL.
"This one's lower," said Posada, who had an MRI exam Tuesday.
To fill his roster spot, New York recalled catcher Francisco Cervelli from Double-A Trenton. Regular backup Jose Molina takes over as the team's starting catcher, a role he filled admirably while Posada was injured last season.
Molina provides a defensive upgrade, but Posada's offense and leadership will be missed. On a team full of stars, Posada is arguably the Yankees' most indispensable player.
"It's tough. He's one of the guys who knows how to win," teammate Johnny Damon said. "He's been getting some key hits for us lately. We're definitely going to miss his bat, miss his presence, and we just have to keep going."
The 37-year-old Posada was off to an excellent start, batting .312 with five homers and a team-leading 20 RBI. He thinks it's too early to tell whether he'll be able to come off the DL as soon as he's eligible.
"Hamstrings can be tricky," Yankees manager Joe Girardi said. "I guess if you look at the positive side of it, at least he didn't hurt his shoulder again."
Posada joined six other New York players on the disabled list, most of them key components. Star slugger Alex Rodriguez is expected back soon following March 9 hip surgery, perhaps by Friday.