The band was in Japan last weekend to perform at the annual Summer Sonic Festivals in Tokyo and Osaka. Lead singer Deryck Whibley was drinking in an Osaka bar with friends when, according to various media reports, three men attacked him.

The attack aggravated a slipped disk injury that occurred in 2007.

From Sum41.com:

“Being a part of the Warped Tour this summer meant a lot to us. We haven’t toured in two years and the bands, the crowds and the entire Warped Tour crew have been amazing to us,” said drummer Steve Jocz late last night. “We were excited to be back in front of our fans and are very disappointed that we have to pull off the tour. We know that it would be more frustrating for the fans if we can’t give it our all. Deryck is doing everything he can to get himself better and we’re there for him.”

Click here for the Sum 41 website.