You are so blind it's pathetic. He never mentioned that his knees were giving him issues during the match, if they did after a few matches then he should withdraw from the grass season too since it's even worse on the knees with the low bounce. Even before the tournament it's obvious that he was using this tournament as a preparation for the grass season, it's disrespectful and pathetic. He would have never withdraw during Wimbledon in the exact same scenario. He will pay for it by losing the slam record. On TV some commentators are saying that he might get fined. Good luck to your hero Frauderer.