I've broken a collarbone before. I noticed they said he would miss 4-6 weeks. He should be able to get back on and ride a bicycle today. The problem is that the aerodynamic position that a rider uses (shoulders hunched forward) is exactly the opposite of the way a collarbone is set to heal. Hence the 4-6 weeks. He should be able to ride a stationary during the 4-6 weeks to keep up his conditioning.