Recovery from a serious injury is psychological as well as physical. It is well known that players returning from ACL surgery are medically cleared to return to play long before they return to their pre-injury level of performance (there is a range here with Peterson being exceptional). Gronk is returning from two serious injuries, with the ACL and the arm, which was broken twice and also had an infection which required additional surgeries. He will probably wear the protective brace for as long as he plays because he has a plate in his arm and the brace protects him from breaking the arm again at the plate margin (which he did already before he wore the brace, as I recall). He needs to reacquaint his body and mind with the speed and rigors of NFL football, and he needs to gain confidence in his repaired arm and knee, which will come with each action he sees. The brace on his arm is pretty far down the list of reasons for him not being up to full speed his first game back.