Dice-K was placed on the 15-day disabled list Tuesday, a day after the right-hander allowed five runs in one-plus inning and failed to retire a batter in the second inning of a 6-1 loss to the Oakland Athletics. The injury is along the trapezius muscle on the right side of his neck.
"Dice-K, that neck thing, we're going to try to give it some more time and see if it goes away for good this time," Valentine said. "It's always serious when you have an injury, but it wasn't so serious that he didn't think he could pitch yesterday. It's hard to lift up, it kind of grabs. Sometimes it loosens up."
The pitcher is scheduled to resume rehab upon returning to Boston this week. Valentine wasn't sure if he would need another injection to aid healing and calm down any inflammation.
In hindsight, Valentine said he might have pulled Matsuzaka sooner rather than having him start the second inning if he had known the neck was bothering him.
"That was my fault," the skipper said. "I should have trusted what I was seeing."
Boston recalled infielder Mauro Gomez from Triple-A Pawtucket for a second big league stint this season to fill Dice-K's roster spot and give the Red Sox an extra bat as third baseman Will Middlebrooks nurses a hurt left hamstring. The DL remains a possibility if Middlebrooks doesn't improve in the coming days.
"There's no telling [how long]," Valentine said of Middlebrooks' timetable. "He's coming along. He's a little better today than he was yesterday. That's progress. We have the DL sitting there and we can back date it if we want if we feel there's not enough progress being made during that DL time."
Middlebrooks was able to touch his toes Monday without any spasm or grabbing, which Valentine called "one of those hamstring telltale signs."
Gomez hit safely in his last 10 games at Triple-A, batting .425 (17 for 40). Valentine said he might play some third base, too.
"It's an important opportunity for me to try to stay in the big leagues," Gomez said. "In the minor leagues, I established a good rhythm from the plate hitting to center field and right."
Also Tuesday, Boston reached a contract termination settlement with pitcher Bobby Jenks and granted his unconditional release.
Valentine said the rotation for this weekend's series with the Yankees at Fenway Park is tentatively set: Josh Beckett on Friday, Franklin Morales and Felix Doubront will pitch Saturday's day-night doubleheader and Jon Lester on Sunday. Aaron Cook will pitch Wednesday's series finale at Oakland, while Morales was available out of the bullpen Tuesday and Wednesday if needed.
Jacoby Ellsbury, on the 60-day disabled list with a right shoulder injury suffered in early April sliding into second base, was set to travel to Portland, Maine, to join the Double-A affiliate Sea Dogs. There's no set number of games yet for him to play.
"He's starting all over, really, 16 weeks later," Valentine said. "It's an amount of time, I would think, if he was in an incubator at least the amount of time where they've gotten to see and react to most pitches - the hard one inside, the slider away, the slow one in the dirt."
Valentine expects to add a pitcher to the roster for the weekend, when teams can carry 26 players.