Tom Johnston will not tour with the Doobie Brothers on the upcoming leg of their 50th-anniversary tour due to a back injury.

According to a press release, Johnston is scheduled to undergo surgery and, as advised by doctors, "should not be performing at this time." The tour will proceed with Pat Simmons, Michael McDonald and John McFee, beginning May 25 in Hollywood, Florida. Johnston is expected to return to the stage after he recovers.

"I hope for a speedy recovery and can't wait to get back on the road and continue doing what I love," Johnston said in a statement. "I would like to thank Pat, Michael, John and the entire Doobie Brothers band for covering for me while I recover from back surgery. ... I'm sure they will bring it every night as they always do."

The Doobie Brothers will be on the road through October, with dates scheduled across the U.S. and Canada. "Having all of us together doing these shows I think creates more of a mystique," Simmons told UCR last year. "People are getting it. They realize, 'Hey, I've gotta go see these guys. Gosh, it was the '70s and now they're in their 70s!'"

"I know for me personally, it's just plain fun," he noted. "It always has been, but this is one of those memorable moments in my life and career, having these two guys playing together with me. It's certainly something that I'll carry with me forever."

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