If he needs it for medical reasons, why not -- as long as he isn't hoping for a happy ending. Send him to a 60-year old male sports masseur, not a 25-year old blonde female, though, and that should remove any question you have.
You might be better off asking your doctor than asking here.
The massage therapist would need a signed parental consent form and would take a detailed consultation to try to establish any contraindications to treatment. If there is any doubt about treating because of a pre-existing medical condition then signed consent from their General Practitioner would be required too.
I would have him evaluated by a sports medicine Dr first. at 13 and playing football, there could be other things going on besides just a few sore muscles