BOSTON — Struggling Red Sox starter Daisuke Matsuzaka went on the 15-day disabled list today and could be sidelined much longer.

"This is not going to be a two-week DL," manager Terry Francona said. "We have to figure this out. We have a lot of work ahead of us to get him back to being Daisuke."

In eight starts, Matsuzaka is 1-5 with an 8.23 ERA and an opponents' batting average of .378. Last season, he was 18-3 with a 2.90 ERA and a major league-best .211 batting average by opponents.

He went on the disabled list with a mild right shoulder strain after an MRI on Saturday showed no structural damage. On Friday night, he allowed six runs in four-plus innings of an 8-2 loss to Atlanta.

"He's got some shoulder weakness," Francona said before Sunday's game against the Braves. "I don't know that you can give him a week off and say, 'Come back and pitch and your shoulder's going to be miraculously strong.'"

Before putting Matsuzaka on the disabled list for the second time this season, the Red Sox already had scheduled John Smoltz to pitch in his spot Thursday at Washington. It would be the first major league outing of the season for Smoltz, who had six rehab starts after offseason shoulder surgery.

The Red Sox recalled catcher Dusty Brown from Triple-A Pawtucket to take Matsuzaka's roster spot.

Dice-K is in the third season of a six-year, $52 million contract he signed after the Red Sox paid $51.11 million for the right to negotiate with the Japanese star. This March he repeated as MVP in the second World Baseball Classic, but missed much of Boston's spring training.

"It's hard," Francona said. "We never were really able to get that foundation. And he's alluded to that, too. We've got to get that figured out because it's obviously not working."

After the WBC, Matsuzaka finished spring training with Boston but went 0-1 with a 12.79 ERA in two starts before going on the disabled list with a mild right shoulder strain from April 15 to May 22.

In his first game back, he allowed four runs and five hits in five innings of a 5-3 loss to the New York Mets.

In his last game, he gave up three hits on the first four pitches, including Nate McLouth's homer on the first pitch of the game. He hasn't reached the seventh inning in any of his nine starts.

"If I keep going like this, I have no right to be a part of this rotation," Matsuzaka said through a translator after the game.

Francona stayed late at Fenway Park on Friday, meeting with general manager Theo Epstein and pitching coach John Farrell. Then Francona met Saturday with Matsuzaka and announced that he would be removed from the rotation.

"It all started with the WBC," Francona said Saturday. "It's become obvious that his velocity wasn't what it was."

The 27-year-old Brown hit .239 with two homers and 12 RBIs in 47 games with Pawtucket before reaching the majors for the first time Sunday.