Your concern is valid...too much stress will keep pulling the tendon off the bone, but no stress won't be good either (see this article on
Antifragility. The challenge is for this student to find the Goldilocks' position, but to do that safely, he will need to start very gently, going very shallow into each pose and not holding too long. Constant monitoring how it feels while in the pose, while coming out and the next day will give him some indication whether he is doing too much, or not enough.
Good luck!
Bernie