If he becomes depressed or suicidal and self-harms, get him help regardless of whether he wants it or not.
When he is ready to accept help, try and get him to read/do this:
First I think you should try looking at who you are as a person, in relation to those around you. Look at how your friends and family, see you. Write about yourself in the context in which they see you. Remember that this is a positive experience and look for the highlights of your life and how the people around you treated you. Eg: At christmas time, all laughing and telling stories, my friends and family listened to me and enjoyed my company. I have a good sense of humour." You need to see yourself as being more than basketball.
For the pain and discomfort try simple tai chi, you can find instructional videos on youtube. Tai chi is brilliant because it uses fluid motion that minimises pain and strengthens your muscles. It is also done to 60bpm music that mimics the resting heart rate. This will promote relaxation.
Try using a thought journal to recognise when your thoughts aren't helpful and to help change them.
Situation: You need to describe the situation, it may be helpful to include who you were with as well as what you were doing. For instance "I hurt myself and now I can't play basketball".
Feeling: Here you identify all of your feelings. You should aim to give them a percentage rating as well. For instance: sad 20%, scared 60% Hopeless 20%
Automatic Negative Thought: Here you identify your automatic negative thought: "I can't ever go back to playing basketball. My life is ruined. Nothing good will ever happen to me"
Evidence to support this thought: eg: "I have read stories about washed up athletes".
Evidence that doesn't support this thought: "My friends like me for more reasons than basketball. My life isn't over just because I injured myself. I have more going for me than just basketball.
Alternative thought (more realistic thought): "I can work towards going back to basketball and also try some exciting new challenges"
New feeling: "Relieved 50%, anxious 40%, sad 10%
The thought journal doesn't necessarily "fix" the feelings, as you are probably still going to experience feelings of sadness etc about the thing that has happened. It is designed to promote more realistic or helpful thought processes as opposed to purely pessimistic processes. At the moment, it is likely that you aren't able to see a way out of everything, as you can't think of an alternative. By breaking everything down in this way, you are taking some emotion out of the situation and thinking critically about what actually happened.