One Direction's Niall Horan has got a long rest ahead of him.

The 20 year-old had to go undergo surgery for an issue with his knee which he has suffered from since childhood.

Horan blew out his knee this past December (2013) and the injury was thought to be that severe, an operation was the best cause of action.

The English newspaper 'The Sun' photographed the recovering singer walking on a set of crutches when returning to the UK.

On Friday Niall took to twitter to inform his legions of fans the status of his health.

"Hey guys I know most of you have seen those pics today! Yes I've had major knee surgery , a much larger surgery than first anticipated," he posted.

Adding, "But I would like to tell u , it was a complete success ! Considering the scale of it!"

The main concern for the former X-Factor contestant is to now rest and heel up in time for their tour later this year, 1D will be hitting the road for their 'Where We Are' tour.

The 65-show tour will be starting in April in Bogotá, Colombia before the boys return to the UK for a string of shows in May, and eventually wrapping things up on October 5th in Miami, Fl.

"So all I ask of you guys is that you would respect my privacy as I try to recover and get for the where we are tour!" he tweeted.

BBC Newsbeat also reports, One Direction are releasing two books this year after signing a deal HarperCollins to publish an official autobiography and 'One Direction: The Official Annual 2015.'

2014 is going to be, once again, a big year for One Direction!

Niall Horan
Horan confirmed he had knee surgery via twitter