BOSTON -- Pedro Martinez was listed as day-to-day after missing his start Tuesday night against the New York Yankees with a mild strain of a back muscle.

	Martinez

An MRI exam showed the strain in the latissimus dorsi, which runs from the back and around the side.

Dr. Bill Morgan, the Red Sox team physician, said he will monitor Martinez over the next few days to see how he responds. The team was unsure Wednesday if Martinez will make his next scheduled start Monday afternoon in Yankee Stadium.

"I think the word we got from the MRI was as good as we could expect to get," Boston manager Grady Little said after the Red Sox beat the Yankees 10-7. "Hopefully, he will be ready to make his start next week."

Martinez felt pain Monday when he was playing catch in the outfield before the opener of Boston's three-game series against New York, Little said.

An MRI was performed at St. Elizabeth's Hospital during Tuesday's game.

"We're always concerned about our ace," general manager Theo Epstein said. "But he's in great condition. His shoulder feels terrific and this is a setback, but we all hope it's going to be a very brief one."

Martinez is 4-2 with a 2.83 ERA. Bruce Chen, 0-0 with a 2.70 ERA in three relief appearances for Boston, started in his place and gave up three runs and left with a 4-3 lead after four innings.

Little said Martinez would not return before Monday. "We don't want him to go back out there until he is ready to," the manager said.

In showing the affected area, Little pointed to a spot beneath his own right shoulder blade. The affected muscle, the latissimus dorsi, runs from the back and around the side.

Morgan said an injury Martinez struggled with in the 1999 AL division series against Cleveland involved a different area of the back.

In that series, he pitched four shutout innings in Game 1 and left with a 2-0 lead and a back strain. He won the decisive fifth game in relief with six hitless innings, eight strikeouts and three walks.

Little said Martinez no longer was affected by a groin injury that bothered him but never forced him to miss a start. The new injury is unlike any the pitcher has had, Little said.

Yankees manager Joe Torre didn't change his lineup when the left-handed Chen stepped in for the right-handed Martinez.

"To me, he's still the best," Torre said. "Any time he's not pitching, you think you've got a better shot."

"I'm sure certain guys, especially the right-handed hitters, had their moods elevated today, but they understand how tough it is to win, especially after what we've been through."

The Yankees lost three straight games before beating Boston 7-3 Monday night.

The Red Sox have been careful with Martinez. He was healthy last season, when he went 20-4 with a 2.26 ERA that led the AL. But he spent time on the disabled list in each of the previous three seasons.

"If he went out there and threw and it escalates, then you could have some problems," Boston right fielder Trot Nixon said. "I think that's what the Red Sox are trying to avoid."

In his last outing, Martinez allowed five hits, struck out eight and walked one in six shutout innings as Boston beat Texas 12-3 last Thursday.

The Red Sox claimed Chen off waivers from Houston on May 7. He didn't learn he was starting until three hours before the game.

"Even when I'm relieving, it's short notice," he said. "I like starting but I came here and they were very honest with me. They said that I was going to be in the 'pen."