I am sensing something dubious here. It was "leaked" that he had something worse than a Grade 1 ligament sprain. If that is true, I don't see how it is possible that he is ready to compete in an NBA game just 13 days later. Probably, that leak is simply not accurate, it was put out there to mess with the Celtics, throw them off the scent so to speak.
In any case, I will be surprised if he is full strength. If he is, if he looks normal, you know that the Sixers were playing games with their injury reports. I hope for his sake though, that they are not putting him at risk. I am sure he wants to play, that he is pushing to get back on the court. But 13 days is a really short amount of time for healing.