CHICAGO -- The depleted Boston Red Sox arrived at Comiskey Park to start a three-game series Friday night with their ace Pedro Martinez a reluctant addition to a lengthy disabled list.

Martinez, the reigning AL Cy Young winner, has not been the dominating pitcher everyone has come to expect over his four last starts.

He was sent to the sidelines with a strained left oblique muscle and did not accompany the Red Sox to Chicago, where he had originally been scheduled to start Saturday's game.

He's slated to be checked out by the team's medical staff and rejoin Boston in Minneapolis on Monday.

"I did what I could to pitch. I was tight last time. This time, I feel fine," Martinez said Thursday night after he was put on the DL over his wishes. He can come off July 11, the day of the All-Star game.

"He didn't want to go, he's that type of player," Red Sox reliever Rod Beck said before Friday's game as Martinez's locker sat empty.

"He feels he could do it, he feels he could go out there. We'd rather have him later at full strength. He's not as dominant. But at 80 percent, he's more dominant than most of us. He's amazing."

Martinez was 9-3 with a 1.44 ERA after last Sunday's 6-5, 13-inning loss in Toronto. He still leads the majors in ERA and the AL with 140 strikeouts but has allowed six homers in his last two starts after giving up just three all season.

"Pedro just does it day in and day out. That's how good he is. That's what concerned the club, that he wasn't going to be able to do that," Beck added.

Manager Jimy Williams said he had no problem with Martinez not wanting to go on the DL. The move was made, he said, to clear up any medical problems now as the Red Sox battled the Yankees and Blue Jays in the AL East.

"I think it's the right thing to do and he doesn't," Williams said. "That's all right."

Williams wouldn't reveal Friday who his Saturday starter would be, only to say he wasn't presently with the Red Sox.

Outfielders Troy O'Leary and Trot Nixon are also on the Red Sox DL, as is starter Jeff Fassero. Additionally, outfielder Darren Lewis is slowed by a hamstring injury and Carl Everett was having problems following a root-canal procedure.

The Red Sox did make a deal Friday, acquiring veteran third baseman Ed Sprague from the San Diego Padres for two minor league prospects.