PEORIA, Ariz. -- Veteran left-hander Nate Robertson will have arthroscopic surgery on his left elbow Wednesday and be out for at least four weeks, the Mariners announced Monday.
Robertson, 33, is a non-roster invitee who was competing for the fifth spot in the Mariners' starting rotation. He will have surgery in Los Angeles by Dr. Neal ElAttrache, the Dodgers' team orthopedist who has performed previous surgeries on Robertson's elbow.
Robertson said the elbow has bothered him in his last two outings, and tests showed bone chips that need to be cleaned out. He's had three prior surgeries on the same elbow, the last in 2009.
Robertson said 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, which he estimates will be June before he's ready to compete at the Major Level.
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"It's terrible timing for me trying to make the club, but I'm in good hands," Robertson said. "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. Once I get healthy, then that evaluation process starts. And hopefully it starts soon."
In three Cactus League starts, he had gone 0-1 with a 7.71 ERA in seven innings of work, with 11 hits, two walks and seven strikeouts.
With Robertson unable to even begin throwing again for about four weeks, the Mariners' fifth starter now boils down to a battle between top rookie prospect Michael Pineda and returning veterans Luke French and David Pauley, all of whom have thrown well this spring.
Robertson has a 57-77 career mark with a 5.01 ERA over 223 appearances. He was with Florida and Philadelphia last season after previously pitching seven seasons in Detroit.