He announced it on his Twitter.
Tweet: "Sorry, my friends, I can't play at Queens. The pain on my knee has made me decide to withdraw. I'll try to get to Wimbledon in the best condition possible."
Hopefully he'll be ready for Wimbledon
This means that Gilles Simon is bumped to 4th seed at Queens. First seed will be Murray, second Jo, third Tipsarevic.