Federer had been secretly suffering with back and leg injuries since losing the final of Gerry Weber Open to fellow former world no.1 Lleyton Hewitt in Halle two and a half weeks ago and has not been fully fit throughout the Championships.
“I'm definitely struggling at the moment," said 29-year-old Federer who also fell in the quarterfinals at the French Open. "I'm unhappy with the way I'm playing, I couldn't play the way I wanted.
“I'm struggling with a little bit of a back and a leg problem. They don't allow me to play the way I would like to. The leg issue came in the final of Halle and returned a little bit after my first-round match here. It went away again but just kept creeping back during the matches.
“For the last fix or six days the back has been really badly. It's normal that the back tends to get stiff in the grass-court season but it's just not nice when it doesn't go away and you can't play freely. That's what I was missing today.”
Federer does not expect to play again for more than a month until the year’s next Masters 1000 series event, Canada’s Rogers Cup, which begins on August 9. He will then defend his title at the Western and Southern Financial Group Masters which starts in Cincinnati on August 15 before moving on to the US Open where he will be aiming for a sixth title in seven years.
"I'm looking forward to a rest and then I'll attack again in North America,” vowed Federer. “Reaching the quarterfinals is a decent result. Obviously some people think it's shocking, but many players would die to play a Grand Slam quarterfinal.
"I don't think I played poorly but he went after it. I was not able to defend well enough and he played well when he had to - it was brutal for me. Every time he had a chance, he took it."