5% may actually be somewhat accurate. Faking injuries seems to have become a sophisticated tactic of deception. Nadal may be the best at it. Knee injury timeout while losing vs. Petzschner at Wimbledon and last year's "worst pain ever" before day one of the tourney in the elevator - then he plays a six hour final two weeks later.
"He looked like he was trying to imitate Sampras when I first played him." Agassi in Facing Federer