although im no MD, let me throw my 2 cents in...whenever anyone is thinking about doing gear, it is common practice to have a strict 3-6 months in the gym to allow the body time to get used to the strain and tears on the muscles/joints/ligaments and once you go on gear, you train 10x harder than normal which causes that much more strain and tear...now coming off an injury poses an issue...although he is fully recovered, he had a lapse of 8 months from the gym and has only been back for 2 solid months now...after that much time off, the body has to get used to the abuse working out does to it and if he goes on gear now, 1. his body might not be able to handle the load put on it and 2. by pushing the limits this soon because of gear, he might come to find out that although the injury is fully healed, it might not be able to take the stress and he could reinjure himself...so IMO, it's better to wait a good 6 months after an injury to see how the body reacts to the regular training workload before intensifying it that much more
and to the muscle memory point...yes, muscle memory is good but that doesn't have anything to do with your tendons,ligaments and joints because trust me, i suffer with tendon and ligament damage every day of the week in both of my knees and shoulders...better to be safe than sorry is all i'm saying so take it for what it's worth