If I remember correctly, the dog from Air Bud also died from cancer. A substitute took his place in the sequal of the movie.

I don't know any injuries that can come out of this, except maybe the nose ones that wolfsoul mentionned. I'm not too sure how you can get him into it. It always helps if your dog has a high ball drive.

Mickey can score in soccer. If you bounce it in front of him and say "Score" he'll jump and tap it in with his nose. It's very cute and he loves it Maybe doing the same thing would help. I just got him into hitting the ball with his nose/head by bouncing it in front of him and saying "Pass" he passed it to me. Then when we get in front of the net and I say "Score" he 'passes' the ball to the net. Good luck