he is not quick enough anymore to do it ....... to many ankle and knee injuries.
I don't think it's that. I think his quickness and strength are fine.
His two problems are that he doesn't like to give up even when he's being tackled, which often results in lower-body injuries, and he tries too hard to hit the home run. He has the ability to take punts back all the way, but it's usually either hit it big or strike out for him because he tries to dance and dodge too much looking for that big play.
You can see these thing in his punt return numbers. He averaged 14.3 yards per return as a rookie, primarily thanks to two big returns including a 93-yarder. The next year he returned the same amount of punts (15) and averaged 6.9. His last year to return punts he averaged 5.5 per return, with a long of 44.
On punt returns, you need someone with the ability to take it all the way back but also understands how to squeeze out all the yards he can when it's just not possible to make the big return. That's one reason good punt returners aren't easy to find.