You have to wonder too if it could be that your teammate/friend has something on his mind that is keeping him from performing under pressure. Perhaps try asking him how he's doing in whatever way you feel comfortable, maybe his parents are going through a divorce, he's doing terrible in school, has relationship trouble? My two cents are that it never hurts to ask and he'll feel more included in the team dynamic if you do because he knows you care how he's doing and how he's performing. Plus he probably has the pressure of sensing that everyone on the team expects him to perform because he has the ability, so taking the pressure off him might actually help him do better since he is probably blowing up mentally, and then as a result blowing out physically. The mind is a powerful thing! Just a thought from someone who was once that guy not performing and then had people I could count on to help me focus on what was important: fun and team camaraderie.