One Direction heartthrob Liam Paynehad to pay a visit to A&E during band mate Niall Horan's Las Vegas birthday bash, according to reports.

The 1D singer was in Sin City with his Irish BFF to celebrate his 21st birthday, when he apparently had a fall leaving his arm in a cast.

A source told MailOnline that the singer hurt himself 'while break dancing', however a rep for the star told the Mirror it was a 'training' injury.

Though we've not spotted any comments from the boys themselves, a pic of Liam in a roof top pool shows a cast on his right arm, not that it hampered his evening!

It was a star-studded affair for Niall's birthday, so much so that Joe Jonas even bumped into him in the loos!

'Always nice running into @NiallOfficial when he is on the toilet.. [embarassed emoji],' he tweeted.