Elon Musk tweeted on Tuesday that "I'm not buying any sports teams", calling a viral post about him purchasing Manchester United a joke.

The world's richest man has a habit of posting provocative statements on Twitter for fun and Musk was at it again when he told his more than 103 million followers: "Also, I'm buying Manchester United ur welcome."

The billionaire Tesla and SpaceX CEO made the comment in reply to another of his tweets, about supporting both of the United States' two major political parties.

The 51-year-old, who is embroiled in a lawsuit over his bid to buy Twitter, was subsequently asked on the platform if he was serious about owning Manchester United.

"No, this is a long-running joke on Twitter. I'm not buying any sports teams," Musk replied, after his original tweet garnered nearly 500,000 "likes" in a matter of hours.

"Although, if it were any team, it would be Man U. They were my fav team as a kid."

Manchester United, one of the biggest clubs in world football but suffering a prolonged slump, are owned by the Glazer family.

There was no immediate reaction from United or its owners to Musk's tweets.

Shares of the team listed on the New York Stock Exchange are down year to date, but ended Tuesday flat, with a market capitalisation of US$2.1 billion.

Despite calling it a joke, Musk's tweet could land him in trouble with US regulators.

Musk, who recently sold nearly US$7 billion worth of Tesla shares, is in a major legal battle in the US state of Delaware over his aborted plan to buy Twitter. (AFP)