BOSTON – Just when the Boston Red Sox are getting some of their best hitters back from injury, they’ve lost another one of their best for the season.

First baseman Kevin Youkilis is scheduled to have season-ending surgery today in Cleveland for a torn muscle in his right thumb. He left Monday night’s 6-5 loss to the Indians with the injury.

“I think Youkilis was pretty resolved to the fact this was probably what was going to happen,” Manager Terry Francona said before the finale of the four-game series with Cleveland.

Batting cleanup for most of the season, Youkilis is hitting .307 with 19 homers and 62 RBI. Francona said that Mike Lowell, who came off the disabled list when Youkilis went on it Tuesday, is expected to play at least four of the next five games at first base.

Center fielder Jacoby Ellsbury returned to the lineup on Wednesday after broken ribs limited him to nine games all season. Catcher Victor Martinez was sidelined for 23 games with a broken left thumb before returning July 26. And Lowell missed 34 games with a strained right hip.

But several key players remain sidelined.

Second baseman Dustin Pedroia has missed 34 games with a broken left foot, and catcher Jason Varitek has missed 30 with a fractured right foot. Pedroia, the 2008 AL MVP, has been jogging and taking batting practice but can’t run without pain.

Center fielder Mike Cameron went on the disabled list Monday with a lower abdominal strain.