Boston, MA (My Sportsbook) - The Boston Red Sox scratched ace righthander Pedro Martinez from Tuesday night's start against the New York Yankees because of a suspected strained right latissimus muscle.

Martinez, who is 4-2 on the year with a 2.83 ERA on the year, is expected to have an MRI in the next day or two to determine the severity of the injury. He felt the pain near his right shoulder blade Monday while tossing the ball in the outfield before the start of the three-game set against the Yankees at Fenway Park.

"With Pedro, there's always a heightened level of concern for obvious reasons because he's so important to the organization," said Red Sox general manager Theo Epstein. "But it's not panic time. This injury hasn't even been diagnosed yet. All we know is that he's missing this one start."

The injury comes as the Red Sox are one game behind the Yankees for first place in the AL East.

"He wants to be out there on the mound against the New York Yankees," added Epstein. "He doesn't want to miss any start. Like the rest of us, he just wants to get healthy and get back out there as soon as possible."

Epstein said for Martinez to rest now was more important than force him back to the mound this early in the season.

"It's our job to have Pedro pitch as much as possible this season," said Epstein. One start in May is not going to make or break this club. The important thing is Pedro's long-term health."

The injury to Martinez means lefthander Bruce Chen will make his first start since 2002, as he heads to the mound tonight. Chen pitched for the Mets, Expos and Reds that season, appearing in 55 games, including six starts.

Chen was claimed off waivers from the Astros earlier this season after appearing in 11 games for Houston. This will be his fourth outing in a Red Sox uniform.

The Red Sox announced April 7 that they will exercise their club option on Martinez's contract for the 2004 season.

A three-time Cy Young Award winner (1997, 1999, 2000) and a six-time All-Star selection, Martinez has led the league in ERA four times in his career. His career .708 winning percentage (155-64) is best in major league history among pitchers with at least 200 decisions ahead of Whitey Ford (.690).

Also, Rudy Seanez had his contract purchased from Pawtucket and is on Boston's 25-man roster. Jason Shiell was optioned to Pawtucket prior to Tuesday's game.