Ben Spies will not return to Yamaha for the final round of the 2012 season and will also be unable to make his planned Pramac Ducati debut at the Valencia post-race test.

After undergoing surgery to repair a shoulder separation suffered in last Sunday's wet Malaysian Grand Prix, the Texan revealed on Twitter that there was "a little more damage than I thought".

A statement from Yamaha later added: 'The procedure consisted of the reconstruction of the Coracoclavicular Ligaments torn in the crash and a reduction of a separated Acrimioclavicular joint, aided by a Twin Tightrope device, which is a suture based system. Cadavar tissue was placed to replace and reinforce the Coracoclavicular Ligaments that were torn.

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'The surgery was successful, Spies will make a full recovery although he will need to remain in a sling for up to 10-12 weeks'.

That recovery time-frame rules out both the Valencia season finale on November 9-11 and post-race test on the Tuesday and Wednesday.

Spies, just tenth in the championship after a torrid second season at the Factory M1 team, has not been replaced by Yamaha for this weekend's Australian round.

The decision on a replacement rider for Valencia 'will be clarified by Yamaha Factory Racing following the Phillip Island weekend'.