Posada was a last-minute scratch from the New York lineup on Sunday when he felt unable to throw with any velocity. He has been treating a strain to his right subscapularis muscle, but the 36-year-old backstop believes he may have a more serious injury.
"I'm going on the DL," Posada said. "I think we've got to be smart about it. It's not getting any better, so we've got to find out what it really is. The MRIs show a strained muscle, and I think it's more than that. I want to find out."
Posada said that he wants to visit Dr. James Andrews, the noted Birmingham, Ala.-based orthopedic surgeon, though he will first visit with Yankees team physician Dr. Stuart Hershon in New York. The New York Times first reported Posada's injury on Sunday, stating that he has a torn muscle in his shoulder.
"It's very disappointing," Posada said. "It's the biggest disappointment in my career, probably, being on the DL and not being able to participate in games. It's really tough. I thought it was coming along, but it's not. It's something that we've got to find out what's really bothering me and take it from there."
Yankees manager Joe Girardi said that the club had not immediately decided on any roster moves.
"We'll talk about what we're going to do," Girardi said. "It's frustrating, because he threw the ball great [Saturday]. It just didn't come back today. Obviously, we'll have him evaluated when we get back to New York."
Posada was removed from an April 8 game at Kansas City when the Royals stole four bases on him, and after the game, Posada complained of a "dead" feeling in his arm. He underwent an MRI in Kansas City, which was shared with three doctors -- Hershon, Andrews and Reds team physician Dr. Timothy Kremchek -- all of whom diagnosed a strain but no serious structural damage.
Posada had a pinch-hit three-run triple in Saturday's Yankees 4-3 loss to the Indians, and he had said the injury was not affecting him at the plate. He is batting .302 with one home run and 11 RBIs in 18 games, having also seen time at first base and designated hitter.
The Yankees thought that the worst of the shoulder problems was behind them when Posada caught three of New York's last five games entering the weekend, plus four more innings Saturday, but backup Jose Molina was pressed into duty 12 minutes before first pitch Sunday.
Posada said the injury popped back up while he was catching in Saturday's game.
"The first throw felt great, and then the second throw I felt something," Posada said. "Then I threw the ball to third base on a strikeout and it was painful. [Sunday] I got here early and started throwing a little bit, and I couldn't throw."
"He's been fine every day," Girardi said. "He caught two in Chicago and we gave him a day off, and he caught one [in Cleveland]. He had no problems and threw great [Saturday]. It's shocking, in a sense, to me. I'm surprised."
Posada signed a four-year, $52.4 million deal before this season and has said that he intends to catch all four years, but that goal has appeared dubious through New York's first 26 games.
"I'm even apologizing to the Yankees, because I signed a good contract last offseason," Posada said.
Posada was walking through the Yankees' clubhouse Sunday morning with an ice wrap over his right shoulder, notable because he had not yet conducted any baseball activities. After the game, Posada rejected the idea that he might be able to stay in the Yankees' lineup as a first baseman after the disabled list assignment, stating, "I'm not playing first base. I'm a catcher."
Posada's teammates said that the loss would have a significant impact on the club.
"I feel bad. This is a guy we really need in the lineup," second baseman Robinson Cano said. "In yesterday's game, he came up with the bases loaded, hit a line drive and tied the game. That's the kind of guy you need."
"[The loss is] huge, not only on the field, but off the field in his leadership," Joba Chamberlain said. "He'll still be here, and it's going to be different for him because it's never happened. I think he's going to take a bigger leadership role for us young guys and help us. It's a tough loss for us, but I think he's going to be bigger in different ways."
Molina is the Yankees' only remaining catcher on the roster, with veteran Chad Moeller having been designated for assignment on Friday. The Yankees could purchase the contract of 26-year-old Chris Stewart from Triple-A Scranton/Wilkes-Barre to provide an immediate backup for New York on Monday as it completes its four-game series at Cleveland.
Stewart has 23 games of Major League experience in the last two seasons with the White Sox and Rangers, batting .200 in 45 at-bats.
"It's a little tough spot," Girardi said. "We've been in a few of them this year, and we found a way to make it work and get through it. We'll have to get through it."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.