ARENZANO, Italy -- Chris Horner of the United States has withdrawn from the Giro d'Italia on Wednesday because of a muscle tear in his left calf.

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Chris Horner of Bend, Ore.

The Astana team said Horner crashed in Tuesday's 10th stage and needs a week to recover. He is returning home to Bend, Oregon. The crash was not reported by organizers, and the injury was not listed on the daily medical update.

Horner finished 25th in stage 10 -- 1 minute, 39 seconds behind winner Danilo Di Luca -- and was 11th overall, 3:24 behind the Italian.

Horner's withdrawal is a blow for Astana because he has been a key support rider for Levi Leipheimer in his bid to win the Giro. Lance Armstrong also rides for Astana.