BOSTON -- The Yankees respect the talents and work ethic of understudy Wil Nieves, but each game that Jorge Posada misses is a reminder of just how valuable their starting catcher really is.

Posada, 36, missed his second start with a bruised left thumb on Sunday, held out of the lineup with no definitive date for return. That's not good news for the Yankees, who had grown accustomed to Posada's production on both sides of the ball.

"He's crucial," Yankees manager Joe Torre said. "He's one of the offensive parts, the defensive parts, and what he means to the pitching staff. Being a former catcher myself, I put a lot of value into what he does. There are certain key guys."

Posada, who is carrying a 10-game hitting streak and is batting .358 with two home runs and 11 RBIs, has been one of the more unsung heroes of the Yankees' first month.

Posada said that the swelling has subsided only slightly, and as he showed his hands to reporters, Posada's left thumb stands out visibly when compared to the right thumb. Posada said he isn't certain when he'll be able to slip on a glove and receive pitches again, and to compound matters, a return to the lineup will likely mean a return to being pounded.

"When I get back in there, I'm probably going to get a ball off it, too," Posada said. "We'll see what happens. It's just how I can bounce back from it -- that's the biggest thing."

Posada suffered the injury while catching a pitch from starter Andy Pettitte in the first inning of Friday's 7-6 loss at Fenway Park. Posada doubled in the fourth inning off Curt Schilling but was replaced by Nieves in the bottom half, going for precautionary X-rays that revealed no fracture.

"It was just a cutter that didn't cut," said Posada, who is continuing to wear a thumb guard to protect against re-injury. "It got in on the hand. There's not much you can do."

Torre said that the idea of having Posada available to play on Monday against Tampa Bay was "reasonable," but Posada said he'd be ready to swing a bat before he was able to catch.

That option wasn't in play Saturday, as Posada -- originally considered to be a pinch-hitting candidate -- told Torre otherwise. The Yankees could always use Posada as a designated hitter to get him into the lineup, but Torre said they weren't ready to cross that road yet.

"It is frustrating," Posada said. "You want to be out there and you want to play. It's tough."

Not perfect, but good enough: After missing Saturday's affair with lower back pain and a sore left hamstring, Johnny Damon was back in center field at Fenway Park on Sunday.

He wouldn't say he was completely healthy, but that has been nothing new for Damon, who estimates that there have been only about 20 games in his Yankees career in which he's felt really top-notch.

"What really stinks is just always playing beat up," Damon said. "I'm sick and tired of it. Sometimes, I'll be 100 percent, but I'm not sure [when]. In this game, you've got to try to figure things out a bit more, which I'm sure I'm going to."

Damon said that his two outfield dives in his last three games probably played a part in the hamstring issue, but taking a step back to look at the bigger picture, Damon believes that the wide expanses of Fenway Park's center-field area did him no favors.

Yankees Coverage
Jeter's late homer lifts Yanks
Yanks gear up for lesser opponents
Chamberlain springs curve on Sox
Notes: Peace of mind for Posada

Red Sox Coverage
Schilling's gem ends with loss
Bauman: Game mirrors Classic duel
Sox don't take lead for granted
Notes: Matsuzaka pushed back
Season Series
Yankees win 10-8
• 9/16: Yankees 4, Red Sox 3
• 9/15: Red Sox 10,Yankees 1
• 9/14: Yankees 8, Red Sox 7
Previous season series
2006: Yankees 11, Red Sox 8
2005: Yankees 10, Red Sox 9
2004: Red Sox 11, Yankees 8

"Before, when I had to play here [in Boston] and deal with that wall out there, I was pretty healthy for most of the season," Damon said.

"Once you're playing that wall, it seems like there's something all the time. There's always a strong throw you always have to make because you have a chance to throw some guy out at second base on a ball hit off the wall. Hopefully, that changes real soon."

Meet you there: Hideki Matsui is ready and waiting to join the Yankees. The left fielder strained his left hamstring running out a ground ball on April 7 against the Orioles in New York, but he completed his rehab Sunday at the Yankees' Minor League complex on Himes Avenue in Tampa, Fla.

Following rehab games on Friday and Saturday, Matsui took batting practice off a Minor League pitcher Sunday at the complex, spraying 30 pitches around a vacant diamond. He is expected to join the team on Monday at Tropicana Field, and Torre said he would likely use Matsui in the starting lineup.

"He's ready," Torre said.

Sooner or later: Nieves entered play on Sunday still looking for his first hit in a Yankees uniform, with his last Major League safety -- an infield single on Sept. 29, 2002, while playing for the San Diego Padres -- a distant memory.

Nieves came into the 2007 campaign 0-for-10 over brief stints with the Yankees during the last two years, and came into Sunday's game 0-for-12.

While the Yankees are satisfied with Nieves' defense, offense has obviously been a concern, and the team is cheering for him to finally break the skid.

"I think he senses the anxiousness from everybody around him," Torre said. "Every time he gets up there, he's got all these cheerleaders in the dugout who pat him on the back every time he comes back."

Quotable: "I think they'd like to be in my shoes. I'm living my childhood dream." -- Damon, on the booing Fenway faithful

Coming up: The Yankees will make their way back to Florida's Gulf Coast area on Monday, heading to the Tampa-St. Petersburg area for the first time since breaking Spring Training on March 31.

Left-hander Kei Igawa (1-0, 6.06 ERA) will make his fourth start of the season, coming off his first Major League victory on April 18 at Yankee Stadium. Left-hander Casey Fossum (1-1, 6.11 ERA), a former touted Red Sox prospect, will get the call for the Devil Rays, with first pitch scheduled for 7:10 p.m. ET.