My case is slightly different as it was my leg but when I had an operation recently I wondered about driving. Nobody had told me I wasn't to drive so I asked the nurse who was doing my dressings. She advised me that if I wasn't able to stamp my foot on the floor without pain then I could not drive. If I had chosen to drive and had an accident, the chances are my insurance would not pay out. So perhaps it's the same, if he could not perform an emergency stop without pain, then he shouldn't be driving.