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02/28/09 2:00 PM EST

Posada out of Saturday's lineup

Catcher says he tweaked shoulder while stretching Thursday

TAMPA, Fla. -- Jorge Posada experienced the first setback of his rehab process on Saturday, as the Yankees scratched the designated hitter from the lineup with soreness in his surgically repaired right shoulder.

Posada said that he tweaked the shoulder while stretching in the on-deck circle on Thursday at George M. Steinbrenner Field, but he stressed that he does not feel any pain and is not concerned.

"I played yesterday with it, and I could play today," Posada said. "It doesn't hurt me to throw, and it doesn't hurt me to hit. It's just sore."

Posada homered in his first at-bat that game, and he said he would have played on Saturday against the Twins if the Yankees had let him. He also played on Friday in the club's exhibition game in Fort Myers, Fla.

"Jorgie wants to play; we told him that he's not playing," Yankees manager Joe Girardi said. "If it was the season, he'd probably play."

He was examined by Dr. Chris Ahmad at the ballpark, and Posada said that he expects to be sidelined from throwing drills for two or three days until his strength returns.

"I knew there was going to be soreness," Posada said. "I was expecting it to be a little bit earlier than now. Since everything was going so well, we kept going."

Posada said he performed one stretching exercise that he was not supposed to, bringing the bat up over his head and behind his neck, when he felt something in his shoulder.

But Posada said it did not bother him in batting practice, and his rehab has been mostly uneventful to this point, gathering at-bats as a DH while also catching bullpen sessions.

"It's just a little bump in the road," Posada said. "I think it's going to be fine."

Girardi said that Posada's timetable for appearing in a Spring Training game as a catcher on March 15 is not affected. He will go through a series of exercises with trainer Gene Monahan on Sunday.

Shelley Duncan replaced Posada in the lineup as the designated hitter on Saturday.

Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.