Sum 41 rocker Deryck Whibley has been hospitalised after being attacked in a bar in Japan.

The musician - the ex-husband of Avril Lavigne - was beaten up by three people as he drank with his bandmates.

After being taken to hospital, Deryck underwent an MRI scan and was diagnosed with a slipped disc in his back.

In a statement on the group's website, the band said: "It is unfortunate to say, but Deryck Whibley is still in the hospital.

"He was attacked in Japan. We are waiting for results and we are hoping for the best. Thanks for your support."

The 30-year-old frontman has been told by doctors to cancel his upcoming performances, but Deryck has vowed to play at the Summer Sonic Festival in Osaka and Tokyo this weekend.

A posting on the band's twitter account read: "Despite doctors' instructions, he has decided to play at Summer Sonic regardless."

Police are now investigating the assault.

The group - Deryck, Tom Thacker, Jason McCaslin and Steve Jocz -are in Japan on their 'Warped' tour.

This is the latest piece of bad luck to hit Deryck on the road, as he had to cancel three concerts in the last week after falling ill with bronchitis.