Niall Horan of One Direction had a more serious knee injury than he initially thought, he tweeted Friday.

Horan tore knee ligaments in December. U.K. newspaper The Sun ran a photo of him on crutches at London's Heathrow Airport, which required an explanation to his nearly 17 million Twitter followers.

"Yes I've had major knee surgery, a much larger surgery than first anticipated," Horan wrote. "But I would like to tell u, it was a complete success! Considering the scale of it!"

Don't worry, kids. He'll have plenty of time to heal, as One Direction doesn't have any shows scheduled until late April, when the group starts a South America tour. The boys will play stadiums in the U.S. this summer, beginning Aug. 4 at New Jersey's MetLife Stadium.

Contact Tony Hicks at Facebook.com/BayAreaNewsGroup.TonyHicks or Twitter.com/insertfoot.