Well I don't know if the true nature of his injury is his stomach virus or his knee... or something else. But if this is just fear then I think he's wrong. He needs to play, even if he loses first round. It's not going to get easier if you keep putting it off.
But if he really can't play then that's all there is to it. I wish him luck with his recovery, and there's nothing much else to talk about.
Just leave him alone until he comes back.