Well, at least we know there's something Roger Federer can't do.

Fresh off the court from defeating Kei Nishikori in five sets, the former world No. 1 looked to be expecting a cruisy post-match interview in front of thousands of fans.
What happened was quite the opposite.

Channel Seven commentator Jim Courier outed Federer's singing skills to the world, sharing a video of the 35-year-old champ singing with fellow tennis players Grigor Dimitrov and Tommy Haas on Twitter with the packed Rod Laver Arena.

Federer's singing left a lot to be desired, with Courier stopping the video short.

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"We can wrap, that's enough. That's enough. We've got enough," he said.

"Is this sort of a normal Grand Slam thing that you do and the second question is who has the terrible pitch?

"Who's voice is that? Is that you, are you the poor singer in that group or is that Tommy, be honest?"

Federer was quick with excuses for the sub-par musical performance.

"Oh God. I didn't even know that song that well. I have heard it many times, the lyrics are not my things. That's why I think my voice was playing up a little bit."

Federer will now play Mischa Zverev - who caused a massive upset defeating Andy Murray - in the quarterfinal round.

- news.com.au