Raonic, who had virtually no chance of making into the semi-finals after successive losses this week, says he's been struggling with a quad injury.
"What I was consistently told with this is if I was to step out on court I'd, sort of, be walking a tightrope where I can play obviously not at 100 percent but with a significant risk of losing up to six to eight weeks if things go badly. So losing six to eight weeks of solely rehab sort of means you lose 12 weeks of getting back into shape and everything. Those are definitely significant factors in my decision."
It was Japan's Kei Nishikori downing Raonic's last-minute replacement, David Ferrer, in a 3-set battle.
And Roger Federer has earned a semi-final spot after destroying Britan's Andy Murray in straight sets 6-0, 6-1.
