The Indians announced the moves on Sunday before their home game against the New York Yankees.
Sizemore had struggled at the plate and not played much in the field recently because of the injury. He went 1-for-4, hitting his team-leading ninth homer Saturday night against the Yankees, but is hitting only .223 overall.
A year ago, Sizemore had career highs of 33 homers, 90 RBIs and 38 stolen bases while batting .268.
Gimenez can catch, and was needed as a backup to Kelly Shoppach. He will start in place of Victor Martinez, who left Saturday's game with a left knee contusion.
X-rays were negative and Martinez, batting .350 with seven homers and 36 RBIs, said he hopes to be able to play soon.
"It's very sore and I can't play today, but it feels much better than I thought it would," Martinez said. "When it happened, I was in so much pain.
"I put a lot of ice on it overnight and did a little workout in the training pool this morning. It feels a lot better. Not good, but better."
Martinez fouled off a pitch from former teammate CC Sabathia and rolled around face down in agony Saturday night. He told manager Eric Wedge that he wanted to stay in the game, but needed assistance to get down the dugout steps after grounding out.
Martinez has been splitting time between catcher and first base this season. A year ago, Shoppach got increased playing time and led all AL catchers with 21 homers when he took over for Martinez, who missed more than two months recovering from right elbow surgery.
No move for Martinez
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