OAKLAND, Calif. -- The Boston Red Sox placed pitcher Daisuke Matsuzaka on the 15-day disabled list Tuesday with a strain of his right trapezius muscle.

Matsuzaka experienced tightness in the same muscle, which stretches from the neck to the shoulder, during spring training. The issue flared up again in May while he was rehabbing from Tommy John surgery.

"We're going to try to give it some more time and see if it doesn't go away for good this time," Red Sox manager Bobby Valentine said prior to Tuesday's game against the Oakland Athletics.

Infielder Mauro Gomez was recalled from Triple-A Pawtucket to take Matsuzaka's spot on the roster.

Matsuzaka allowed five runs on four hits and two walks in one-plus innings Monday in a 6-1 loss to the Athletics. He had experienced discomfort leading up to the start, but the injury was thought to be under control.

"It's always serious when you have an injury, but it wasn't so serious that we didn't think he could pitch yesterday," Valentine said.

Valentine regretted not taking Matsuzaka out of Monday's game earlier. With Boston already trailing, 4-1, in the second inning, Valentine visited Matsuzaka on the mound after he allowed a single to Brandon Inge. Matsuzaka walked the next batter, Cliff Pennington, on four pitches and was removed.

"I should have taken him out," Valentine said Tuesday. "When I went to the mound, if he said it was bothering him at all -- because I asked him in between innings -- I would have called the trainer and taken him out at that time.

"I didn't want to get the bullpen up in the second inning. But for an injury, if I knew I could get a guy warmed up and into the game, I probably would have done that. That was my fault. I should have trusted what I was seeing."

The Red Sox still have five starting pitchers on their roster. Jon Lester takes the mound Tuesday against Oakland and also will start Sunday's series finale against the New York Yankees.

Aaron Cook is Wednesday's scheduled starter against the A's while Josh Beckett, Felix Doubront and

Franklin Morales will start the first three games against the Yankees.

After Tuesday night's 3-2 loss to Oakland, the Red Sox optioned right-hander Clayton Mortensen to Triple-A Pawtucket. Righty Justin Germano is expected to join the club Wednesday.

Jimmy Durkin is a contributor to ESPNBoston.com. Information from The Associated Press was used in this report.