By Piers Newbery
BBC Sport at Wimbledon
Roger Federer suffered a blow to his Wimbledon chances despite moving into the last eight with a straight-sets win over Feliciano Lopez.
Federer had looked in superb form on his way into the last 16 and is among the favourites for the title.
But the fourth seed needed extensive on-court treatment for a back problem after just two games and later revealed the problem had not gone away.
"I can't really tell you what happened out there, I just couldn't move any more," he said.
"It was very tough for me and I feel it now, it hasn't gone away. I don't know how I won today.
I have to try and take this lucky match and get rid of this injury and get ready for the quarters
"I was always in a lot of pain. As the match went on it got a little better because the body gets warm and you try to forget it."
Federer will play Sjeng Schalken in the quarter-finals after the Dutchman beat Rainer Schuettler.
"I didn't think that I would sit here as a winner after the shock I had today," he said.
"I have to try and take this lucky match today and get rid of this injury and get ready for the quarters."