From US OPEN site:
Andy Murray, who has taken so many difficult losses to Nadal at the Slams, including in last year’s US Open semifinals, looked pained when discussing the pullout. While almost every player has come into a Grand Slam event at less than 100 percent, it is considered preferable to do that and give oneself an outside chance rather than not being able to show up at all.
“Obviously a shame,” said Murray, the Olympic gold medalist who has a very good chance of passing Nadal for the No. 3 spot in the rankings after the US Open. “I like Rafa a lot as a friend. I'm disappointed for him. I think for tennis and also a major competitions, it's a huge benefit when you have the top players playing. It’s obviously tough for him. He's had trouble with his knees in the past. So I hope he can rest, doesn't come back too early, and gets them fixed so he can get back to playing his best tennis.”
awww, Andy really loves Rafa.
These words from him are so warming and touched my heart, probably Rafa feels same, too.