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04/01/12 1:20 AM ET

Cotts' injury may keep him off roster

GOODYEAR, Ariz. -- Rangers pitcher Neal Cotts' chances of being on the Opening Day roster were dealt a severe blow when he strained a muscle in his left side during his one inning of work against the Indians on Saturday night.

The Rangers are not ready to announce Robbie Ross is on the Opening Day roster, but he is the only healthy left-handed reliever in camp. He will be on the Opening Day roster unless the Rangers go with an all right-handed bullpen that includes Yoshinori Tateyama.

Cotts pitched a scoreless sixth in the Rangers 7-4 victory over the Indians but felt the muscle give on the next to last pitch he threw in the inning. The initial diagnosis is it could be 7-10 days before Cotts can start throwing again.

"He was throwing the ball extremely well," Rangers manager Ron Washington said.

The Rangers open the season on Friday against the White Sox. Cotts will be re-evaluated on Sunday to get a more definitive evaluation of the injury but it's almost certain that he will not be ready for Opening Day.

"I don't think there is ever a good time for an injury," Rangers general manager Jon Daniels said. "He has been throwing the ball great. If that's all it is, there are worse things. He'll bounce back. If he continues to pitch the way he has, he'll pitch for us at some point during the season."

Cotts has not allowed a run in his last five outings, including four Cactus League games. He also had a scoreless inning in a Triple-A game.

T.R. Sullivan is a reporter for MLB.com. Read his blog, Postcards from Elysian Fields and follow him on Twitter @Sullivan_Ranger. This story was not subject to the approval of Major League Baseball or its clubs.