TOKYO, Japan — Sum 41 frontman Deryck Whibley has been hospitalized after he was attacked Thursday night at a bar in Japan.

Whibley, the ex-husband of Avril Lavigne, was assaulted by three unidentified assailants after the band arrived in town for this weekend's Summersonic Music Festival in Osaka.

"It is unfortunate to say, but Deryck Whibley is still in the hospital," the band said late Thursday on their Facebook page. "He was attacked late last night in Japan. We are waiting for results and we are hoping for the best. Thanks for your support."

Japanese police are investigating the incident, but they've yet to make any arrests in the case.

The group posted an update Friday evening, saying, "After an MRI scan, it appears Deryck has slipped a disc in his back once again. Despite doctor's instructions, he has decided to play today's show at Summersonic regardless."

The incident is the latest setback for Sum 41. The Canadian band was also forced to cancel a number of dates on the Warped Tour last week after Whibley came down with bronchitis.