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03/16/11 10:58 PM ET

Robertson out four weeks after surgery

PEORIA, Ariz. -- Veteran left-hander Nate Robertson had arthroscopic surgery on his left elbow at the Kerlan-Jobe Clinic in Los Angeles on Wednesday and will be out at least four weeks, a Mariners spokesman said.

Robertson, 33, is a non-roster invitee who was competing for the fifth spot in the Mariners' starting rotation. The surgery was performed by Dr. Neal ElAttrache, the Dodgers' team orthopedist, who has performed three previous surgeries on Robertson's elbow since 2009.

Dr. ElAttrache removed three bone chips -- one from the front and two from the rear of the elbow. Robertson is expected to return to Mariners' camp on Thursday and begin his rehab with range of motion exercises. The four-week recovery period is the amount of time before Robertson can resume pitching. He'll then have to rebuild arm strength and thus it could be June before he appears in a Major League game.

"It's terrible timing for me trying to make the club, but I'm in good hands," Robertson said the other day.

"Everybody is on the same page about still wanting me to be here, still believing I can help, understanding it's not a career-threatening surgery," he added. "Once I get healthy, then that evaluation process starts. And hopefully it starts soon."

Even so, Robertson said that the Mariners have told him they want him to stay with the organization and see if he can come back and help the club upon his return.

Robertson revealed that the elbow had bothered him in his last two outings, and tests showed the bone chips that needed to be removed.

In three Cactus League starts that encompassed seven innings, he had a 0-1 record and a 7.71 ERA, with 11 hits, two walks and seven strikeouts.

The Mariners' fifth starter battle now is between top rookie prospect Michael Pineda, who started on Wednesday night against the Brewers here, and returning veterans Luke French and David Pauley.

Robertson has a 57-77 career mark with a 5.01 ERA in 223 appearances. He was with Florida and Philadelphia last season after previously pitching seven seasons in Detroit. He was 13-13 and made 32 starts on the 2006 Tigers team that lost to the Cardinals in a five-game World Series.

Barry M. Bloom is national reporter for MLB.com and writes an MLBlog, Boomskie on Baseball. Follow @boomskie on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.