Reigning U.S. Open winner Rafael Nadal announced on Monday that he was withdrawing from the tournament. It marks only the fourth time in the Open Era, which began in 1968, that the defending U.S. Open champion has not appeared in the tournament. "I am sure you understand that it is a very tough moment for me since it is a tournament I love and where I have great memories from fans, the night matches, so many things,” the two-time U.S. Open winner said in a statement. The 27-year-old Spaniard is currently suffering from a right wrist injury, and he hasn't competed since losing in the fourth round of Wimbledon in July. Nadal is one of the tennis' big draw. In his absence, Roger Federer, Andy Murray, and Novak Djokovic will likely vie for the championship.