When the ship sank, he managed to cling to a life boat; his legs freezing in the cold water.
That frost damage led to a doctor recommending he should get his legs amputated. He refused and continued his career. Just 2 years after the sinking of the Titanic, he won 2 US Singles championships, a Wimbledon doubles title, and Olympic gold medal and made it into the International Tennis Hall of Fame.
His story of survival on the boat is pretty amazing, so you should check it out at the source.