Zac Efron has been hospitalised after tearing his anterior cruciate ligament (ACL).

The 31-year-old actor took to social media on Friday (08.02.19) to reveal he has undergone surgery to repair his torn ligament - which is one of a pair of cruciate ligaments in the knee - after he suffered the injury whilst ''shredding the gnar'', a term used when someone excels in extreme sports such as snowboarding, skateboarding, surfing, or skiing.

He wrote: ''I tore my ACL shredding the gnar but all is good. I opted for surgery so I can come back stronger than ever. Thank you to Dr. Kvitne and his team at Kerlan-Jobe Surgery Center. I'll keep you updated as I heal and progress! Thanks for all the love and positivity! (sic)''

The actor - who will next be seen on screens as Ted Bundy in 'Extremely Wicked, Shockingly Evil, and Vile' - is known for his love of the outdoors, and once came face to face with a grizzly bear whilst on a hiking trip in Montana with his brother Dylan.

He said: ''Out of nowhere, [we were like] 'Okay, that's a bear. Everybody stop. And we all stood still. Somebody silently whispered 'But it's charging at us.' It took like two big canters at us.

''[Luckily it] disappeared behind some trees. It was the scariest part of the trip! But it was cool to see a bear that close. It was maybe 15 or 20 feet away. It was charging at us!''

Zac partnered with Columbia Sportswear back in 2017 when he got to test out some of the brand's outdoor gear, and admitted it was a great ''excuse'' for him to see more of the world before he turned 30.

He said at the time: ''I'm about to turn 30, so I'm thinking about how much of the world is left to see, how much there is to do and how much is out there. Luckily this is kind of an excuse for me to get outside even more and follow my dreams and see the rest of the world.''