By Simon Evans
Nadal was knocked out of the Cincinnati Masters by Marcos Baghdatis on Friday, the Cypriot winning the quarter-final 6-4 4-6 6-4.
"My game can improve, that's for sure. It must improve if I really want to have chances to have some opportunity in a week or so in New York," Nadal told reporters after the loss.
The U.S. Open starts on August 30 and Nadal has already targeted his backhand as his problem area.
"I have one week to keep working, keep practicing hard and that's what I am going to try -- to keep improving my confidence with the backhand," he said.
Nadal made 41 unforced errors against Baghdatis, including a surprising 22 on his stronger forehand, but he said that was probably due to him protecting his backhand.
"If my backhand improves all my game will improve," he said. "My movement is going to improve a lot because I won't have to cover the backhand with the forehand and so I will cover positions better on the court.
"I will also be able to make my first serve more calmly because if I miss the serve and he has a return then it will be no problem to play with the backhand.
"But, here, when he had a good return to the backhand, I always started the point in a very bad position... So I think the backhand changed all my game, because I had to make too many adjustments to save that shot.
"But I started to play the backhand with more confidence which is a positive for me," he added.
Nadal was a beaten semi-finalist at the U.S. Open in 2008 and 2009.