Roger Federer coy about viral 'William Tell' video

A grinning Roger Federer evaded questions on Thursday about an online video where he appears to perform a 'William Tell' trick by hitting a can off the head of a man with his powerful serve.  

The YouTube video, posted by Federer's sponsors Gillette, has gone viral in the past 48 hours with more than a million hits to the official version of the clip. 

In the clip, Federer, wearing a business suit, asks a man on the set of an advertisement shoot to put a can on his head and then the ball is shown knocking the can down without harm done. 

Asked if the clip showed a real serve, Federer said: "Well, there's a lot of the debate at the moment. You know how it is with magicians. They don't tell how their tricks work, you know. 

"I don't do it that much, but, yeah, it was shot in one piece and it was ... the guy took a chance. It worked out. I'm happy," he said.                                           

Later, when talking about the clip again, Federer said he had "done it before" but was again asked if the clip showed a real action and he said: "Not saying that. A magician doesn't tell how his tricks work, so ..." 

Federer won his second round match at the Cincinnati Masters on Wednesday after his Uzbek opponent Denis Istomin retired with an ankle injury.