"I'm looking at it as doubtful that he'll be back," said manager Joe Torre.
Mendoza, who has been rehabbing all season from 2004 shoulder surgery, played for the Yankees from 1996-2002, playing a part in all four of Torre's World Series title teams. Mendoza spent the last two years with the Red Sox, getting a championship ring last season after appearing in 27 games.
"Now we have three players from the world champion Boston Red Sox," Torre said, referring to Mendoza, Mark Bellhorn and Alan Embree. "I'm not sure what the odds were on that happening."
Mendoza was 1-0 with a 0.75 ERA in eight games with Columbus, allowing just four hits in 12 innings.
"I worked real hard at Tampa and Columbus," Mendoza said. "I feel good; 100 percent. I'm ready."
Mendoza's first outing for the Yankees didn't go as well as he had hoped. After striking out Richie Sexson, Mendoza allowed an RBI double by Adrian Beltre, then two batters later, Mendoza gave up a two-run homer by Jose Lopez.
"I felt good today, I just made a bad pitch on the home run," Mendoza said. "I wanted it more inside, but it stayed [in the middle]."
"I liked what I saw," said catcher Jorge Posada. "He kept the ball down, he just left a sinker up in the zone for the home run and a changeup up in the zone [for Beltre's double]. He know he's got to keep the ball down."
During his first stint with the Yankees, Mendoza filled a number of roles, from starter to long reliever to setup man.
"He was my wild card, like [Tanyon] Sturtze is now. You could bring him in to the fifth or the eighth," Torre said. "Mendoza was a Yankee for a long time, and he's really come a long way. His velocity has increased, and we all know he can handle the stress of a pennant race."
Tino out: Tino Martinez suffered a minor ribcage strain during his seventh-inning at-bat on Wednesday, an injury which is expected to sideline the first baseman for the next 3-4 days.
"This is the first day, and he's sore," Torre said. "I think it's just a matter of when he's able to do what he needs to do. The good news is that it didn't tear or anything, he just felt something."
Andy Phillips, who was not on the original list of September callups, was brought up from Columbus to give the Yankees another first baseman on the bench.
"Phillips, defensively he's a plus for me," Torre said.
The other callups were left-hander Wayne Franklin and catcher Wil Nieves, while Ruben Sierra was activated from the disabled list.
"With the depth at different positions, you can feel freer to do things earlier," Torre said. "You have to make sure not to get carried away, either. Just because you have players, doing things may not help you win games."
Godzilla the DH: Hideki Matsui was penciled into the lineup as the Yankees' designated hitter on Thursday, as Torre noticed a lack of quickness in the left fielder's bat speed in the past day or two.
"That's all he'll accept," said Torre of the reduced role. "It looks like he's dragging a little bit, so maybe DHing today and not playing until tomorrow night can be a little bit of a lift for him."
Ticket masters: The Yankees have already sold more than 4 million tickets this season, and are now approaching the American League record of 4,057,947 held by the 1993 Blue Jays.
As of Thursday, the Yanks had sold approximately 4,038,000 tickets, an increase of more than 236,000 tickets from a year ago.
"Our fans continue to overwhelm us with their support, and demonstrate why they are the best fans in the world," said Lonn Trost, the club's COO. "Our goal as an organization starts and ends with the fans. Mr. Steinbrenner continues to provide the fans with an exciting team and they recognize his commitment to winning."
On deck: The Yankees travel to Oakland this weekend, where they will play a three-game series against the AL West-leading A's. Friday's opener pits Al Leiter against Dan Haren.