"I broke my collarbone, now it's decision time, to operate or not to operate?" the Garmin-Barracuda rider said on his Twitter feed after a race won by Tom Boonen.
Millar, who admitted doping in 2004, is banned from competing for Britain at the London Games because of a British Olympic Association (BOA) by-law preventing drug cheats from taking part in the Games.
The by-law has been challenged by the World Anti-Doping Agency and the Court of Arbitration for Sport is due to make a decision in April.
