<p><br /> Roger Federer has evaded questions 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.<br /> </p><p><br /> The YouTube video, posted by Federer's sponsors Gillette, has gone viral in the past 48 hours with thousands of fans debating whether it is real or not.<br /> </p><p><br /> 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.<br /> </p><p><br /> 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.<br /> </p><p><br /> "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.<br /> </p><p><br /> 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 ..."<br /> </p>
