CLEVELAND — Grady Sizemore believes he can still help the Cleveland Indians this season after having abdominal surgery.

The three-time All-Star outfielder had a 20-minute hernia operation performed Thursday in Philadelphia by Dr. William Meyers. Sizemore, who is expected to miss four-to-six weeks, went on the disabled list Monday after tweaking his right knee while running out a double in Baltimore on Sunday. It aggravated a bone bruise in the knee sustained while sliding into second base May 10.

He also sustained the abdominal problem on that play two months ago and went on the disabled list. When the knee progressed, the 28-year-old decided to return to the lineup and tried to play through the abdominal discomfort.

“The injury, which resulted in today’s surgery, has been bothering me since the slide in May,” Sizemore said in a statement released by the team. “Knowing the two areas are related and also learning my knee condition is not serious gives me peace of mind going forward that I can finish the season healthy and help contribute to an exciting pennant chase.”

Sizemore has played only 61 games this year, and is batting .237. He has 10 homers, 29 RBIs and no stolen bases. Leading up to the injury, he hit .400 (8-for-20) with two homers, two doubles and four RBIs in his last six games.

Cleveland has been hit hard by injuries, but entered Thursday tied for the AL Central lead with Detroit.

Right fielder Shin-Soo Choo is sidelined by a broken left thumb. Designated hitter Travis Hafner, opening-day starter Fausto Carmona, first baseman Matt LaPorta and others have also been on the disabled list.

Sizemore, who averaged 27 homers, 29 steals and 116 runs from 2005 thru 2008, has spent much of the past three years on the DL. He played hurt in 2009, but after 106 games, he finally had an operation on his left elbow in September. That was followed a few days later by abdominal surgery from Dr. Meyers.

Sizemore played only 33 games a year ago before hurting his left knee — also sliding into second in Baltimore. He had microfracture surgery and began this season on the DL as he continued to recover.

Indians trainer Lonnie Soloff said Sizemore should begin rehabilitation today.

“His prognosis is good,” Soloff said. “We are cautiously optimistic that he will return to full baseball activities in four to six weeks. He should walk as much as a mile starting tomorrow.”

Soloff said that Sizemore’s left knee has held up well despite all the stress put on his body by the other injuries. He also said the two abdominal surgeries are unrelated.

The trainer did say that Sizemore’s all-out style of play leaves him susceptible to injuries, but that it may not be a good idea to tell him to cut down on his hustling.

“Grady plays the game very aggressively and to ask him to change is not easy,” Soloff said. “He’s a unique player. He knows one way, to go all-out all the time.”