I'm a bit more optimistic with the fact time has passed. Had he snapped his ACL, or similar severe injury, that could have been diagnosed as soon as he had a scan, and an announcement with timescale you would have thought would have been made by now. If they're not making an announcement...
So difficult to tell. The whole knee joint can go into like a shock, swell up and show all the signs of a serious ruptured ligament or cartilage, but in fact settle down quite quickly in some cases without any serious damage. Some players experience a stretch of the muscles and ligaments without...