BOSTON – David Wells went on the disabled list for the second time this season Saturday, another blow to the Red Sox rotation after they opened spring training with seven pitchers competing for five starting spots.

That group is down to four with the trade of Bronson Arroyo to Cincinnati and the success of Jonathan Papelbon as the closer. So Lenny DiNardo, who has one start in 30 major league games, probably will fill in for Wells on Monday against Seattle.

Boston replaced the left-handed Wells on the roster with right-handed long reliever Jermaine Van Buren, who was called up from Triple-A Pawtucket.

The Red Sox said Wells has a sprained right knee, which underwent offseason surgery. He received a shot of the joint lubricant Synvisc after Friday night’s win over Seattle. That usually is administered in a series of three injections a week apart. Wells was placed on the 15-day disabled list retroactive to Thursday, meaning he can’t be activated before April 28.

He said he was hurt when he ran to cover first base in his only start this season Wednesday night.

“When you have a bad knee, anything can happen at any given time,” Wells said. “It’s been tender. There’s been good days and bad days.”

Manager Terry Francona and general manager Theo Epstein refused to put a timetable on Wells’ return. Meanwhile, Curt Schilling, Tim Wakefield, Josh Beckett and Matt Clement are the top four starters.

The 42-year-old Wells began his 20th major league season on the disabled list and struggled in a rehabilitation start April 7 at Pawtucket. He struggled again in his first start of the year for Boston last Wednesday in an 8-4 loss to Toronto, allowing seven runs on 10 hits – three of them homers – before leaving with no outs in the fifth.

“I’m going into this with very positive, good thoughts,” he said. “A lot of people have been in this situation and come back and been able to pitch.”

Francona said Wells felt a problem in the knee while throwing Friday.

“I think David felt like it was going to be hard for him to do the things he needs to do to be successful in the condition he’s in right now,” Francona said.

The Red Sox held Wells back during the spring while he rehabilitated his knee, but his last spring training appearance was impressive.

“He didn’t say anything about his knee until now,” Epstein said. “He looked actually pretty good in spring training. I was at his last outing in spring training while the team was in Philadelphia (for two exhibition games) and he looked probably better in that outing than he did at any point last year.

“And then in Pawtucket he struggled, but there were no complaints at all about his knee so you’ve got to factor in what the guy tells you.”

DiNardo was chosen in the Rule 5 draft in 2004, when he made 22 relief appearances with a 4.23 ERA and no record. Last year, he pitched in eight games with one start for Boston with a 1.84 ERA and 0-1 record in 14 2-3 innings.

“We’re comfortable with Lenny spot starting for us,” Epstein said. “He keeps the ball on the ground and this is a chance for him to step up.”

The Red Sox eventually expect the 25-year-old Papelbon to start but don’t want to move him out of the closer’s role, where he converted his first five save opportunities while allowing two hits in 20 at-bats.

“Right now what he gives us is pretty special,” Francona said.

Late in spring training, the Red Sox traded Arroyo for slugging outfielder Wily Mo Pena.

The Red Sox obtained Van Buren in a trade with the Chicago Cubs last Dec. 1. In his only major league experience, Van Buren was 0-2 with a 3.00 ERA in six innings for the Cubs last year but issued nine walks. He was sent to the minors early in spring training this year to work on his control.

“I thought I was going all right,” Van Buren said, “but the real picture was I wasn’t pitching as well as I could so I think that was a good lesson for me to go down and focus on what I really needed to do.”

He pitched four scoreless innings in two relief outings for Pawtucket and allowed three hits and no walks while striking out four.

AP-ES-04-15-06 1821EDT