Player came back from a trial saying he's not good enough

An U13 in our group had a trial last week and wasn't taken on. Since then he's been noticeably quieter and has started comparing himself with the boys who did progress. I don't want to give him the usual 'prove them wrong' speech because that feels like making the next trial the whole point of his football. How would you handle the first couple of weeks after a rejection like this?