Ben Spies has undergone surgery on both shoulders, following last weekend's Indianapolis MotoGP accident.

Sidelined for most of the season with right shoulder issues that began with an accident at Sepang last October, the MotoGP race winner then dislocated his left shoulder in a practice fall during his Indy comeback.

Surgery was required for the new injury, but Spies also underwent more knife-work to tidy up the healing right shoulder, reconstructed last year.

The operation was carried out at North Central Surgical Hospital, Dallas. A statement from the Pramac Ducati team said:

"The intervention, performed by Dr. Daniel Cooper, was intended to repair a fifth-degree dislocation of the left shoulder's acromioclavicular joint and to remove scar tissue from the right shoulder that had already been operated on.

"The procedure was successful, but for the moment, it's not known how long the recovery process will take or when the Texan will return to the track. In addition to the shoulder injury suffered in the fall, Spies also strained ligaments at the base of his left hand."

Spies, who has not raced since round two, is again being replaced for this weekend's Brno round by Ducati test rider Michele Pirro. Spies will surely also miss next weekend's British Grand Prix, with the next race after that at Misano in mid-September.

Former World Superbike champion Spies is in the first year of a two-year contract with Ducati. Team-mate Andrea Iannone is still struggling with a shoulder dislocation from mid-July's German round.