Anybody who has had a knee injury can attest to the fact that even when the doctors clear you and your knee is 100%, mentally is extremely hard to trust it. You plant, but it's always in the back of your mind that maybe it will give out and you just don't plant as hard for awhile. The good news is that with time, you won't think twice about it and you're good to go.
You will never be able to see it and only he will know, but he just won't mentally be all in on his knee for a few weeks and I'm sure the coaches know it.