"He's got some inflammation that we're going to calm down and take whatever time it takes to do it,'' Valentine said. "We thought in between starts was enough time to do it. He could have taken an extra day or two, I guess, but we're going to take the conservative route.''
Valentine said he did not know whether Beckett planned to seek a second opinion or what course of treatment would be prescribed. A cortisone injection is often administered to reduce inflammation.
"Because we have the time, I bet you he will do everything that's necessary to make sure he's going to be as good as he can be when he comes back, I would think,'' Valentine said.
Beckett emerged from the trainer's room just as the clubhouse was closing to the media Saturday and told team publicist Pam Ganley that he would not discuss the injury with reporters.
"They have a pretty good handle on it,'' Valentine said. "If he's going to get a shot or anything, maybe they'll do an MRI so they know the right place to do that.''
Asked the hypothetical question of whether Beckett would pitch if this was Game 7 of the World Series, Valentine said, "Game 1 he would pitch.''
The Red Sox recalled right-handed reliever Clayton Mortensen from Triple-A Pawtucket to take Beckett's roster spot.
Beckett becomes the 18th player placed on the DL by the Red Sox this season. Eleven players are currently on the list, including former All-Stars Jacoby Ellsbury, Andrew Bailey, Carl Crawford, John Lackey and Bobby Jenks.
Beckett's scheduled start on ESPN's "Sunday Night Baseball" against the Chicago Cubs will be taken by left-hander Franklin Morales, who has pitched exclusively in relief since the Red Sox acquired him from the Colorado Rockies last season. Morales, however, began his career with the Rockies as a starter, pitching against the Red Sox in the 2007 World Series.
Beckett missed a start on May 5 with what was described as soreness in his right lat, the large muscle in the back of the shoulder. Valentine said Saturday he did not think the pitcher's current condition was related to that soreness.
This is Beckett's fifth trip to the DL since the Red Sox acquired him from the then-Florida Marlins prior to the 2006 season. He went on the DL and missed 56 games last season with a lower back strain, and also missed time because of a sprained ankle, illness and elbow soreness, though none of those issues required a trip to the DL.
In 2008, Beckett went on the DL and missed 14 games in September with an elbow issue. He also began that season on the DL with a back strain that caused him to miss the season's first six games.
In 2007, he was put on the DL and missed 14 games with a blister on his middle finger.
Beckett was hampered at the start of this season by a thumb issue. Valentine said Saturday that Beckett may have the issue addressed while on the DL instead of waiting until the All-Star break, as originally planned. Beckett may require a cortisone shot in the thumb, according to Valentine.
Valentine said the initial plan was to have Clay Buchholz start Sunday, since he would have been on regular rest due to Thursday's off-day. But the manager said Buchholz told him he would prefer to have the extra rest, and Valentine acquiesced. Buchholz will start Tuesday against the Marlins after another off-day Monday.
"That was plan one,'' Valentine said, "but Clay felt he needed the extra days."
Buchholz has thrown at least seven innings and 100 or more pitches in each of his last four starts, including 125 pitches in a complete-game shutout of the Baltimore Orioles on June 7.
"It's that time of season where guys can get a blow if they can work it in, and I totally understand that,'' Valentine said.
Beckett, 32, is 4-7 with a 4.14 ERA this season. In his last six starts, he is 2-3 with a 2.68 ERA, striking out 30 while walking just six. He has not allowed a home run in his last six starts after giving up nine homers in his first six, including five in his first start against the Detroit Tigers.