Googled on how long it takes for the peroneal muscle and tendon to heal: Patients usually recover fully but this can take considerable time. You must be patient and allow the tendon to heal before going back to activity. If you need surgery, your recovery time may be substantial. You may be instructed not to put your foot down with weight for about six weeks.
I really hope he withdraws from the GPF. 3 weeks is just not enough time.