The difference in meaning is that 'could' suggests it is possible for him to become a top athlete in the future.
'will', expressing the Future Tense, is a prediction that the speaker is asserting he has doubts about - that the future event is INEVITABLE.
A brave assertion by the coach; but yes, 'will' can also be used.
The difference in meaning is that 'could' suggests it is possible for him to become a top athlete in the future.
'will', expressing the Future Tense, is a prediction that the speaker is asserting he has doubts about - that the future event is INEVITABLE.
A brave assertion by the coach; but yes, 'will' can also be used.