My Son Tackled Another Player In A Rugby Game This

My son tackled another player in a rugby game this evening and got the wind knocked out of him when the other players knee caught him in the breadbox. Usually he is fine within a few minutes, but a few hours after the game he started to complain the area being painful to the touch and feeling as though the pain is going straight thru him, out his back. It hurts when he takes a deep breath.