The Scot, who is awaiting a decision from the Court of Arbitration for Sport (CAS) which will determine his eligibility for the Olympics, sustained the injury while riding for Team Garmin-Barracuda in the E3 Harelbeke race.

He wrote on his Twitter page: "I broke my collarbone, now it's decision time, to operate or not to operate?"

He later added: "Operation tomorrow 8:30am.

"Was momentarily put off when surgeon showed me a video of the procedure done on a cadaver.

"Too much info."

Millar, 35, gave no indication of how long he could be out of action.

Given he requires surgery, it could scupper his hopes of competing at London 2012, which remain in the balance after he was banned for doping in 2004, making him subject to a lifetime ban by the British Olympic Association (BOA).

But that stance has been considered "non-compliant" with the World Anti-Doping Agency's (WADA) global code and the case has been considered by the CAS, who are expected to announce their ruling next month.

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