Furthur, the band co-founded by former Grateful Dead guitarist Bob Weir, has had to cancel a tour date after Weir collapsed on stage last week.

Weir collapsed while the group was performing the Dead song “Unbroken Chain” and had to be helped up by two stagehands. He was helped over to a chair and had the strength to play through the rest of the song. Fellow original Dead member Phil Lesh told the crowd at the Capitol Theatre in Port Chester, NY that Weir felt pain in his shoulder.

According to Rolling Stone, Weir returned to the stage the very next day in Atlantic City. He reportedly performed with renewed vigor, as if to prove that nothing was wrong.

Despite that performance though, the group took to Facebook to confirm that they will have to cancel their opening show at the new BottleRock Napa Valley festival on May 9. The statement said that Weir is “unable to perform in any capacity for the next several weeks.”

They still expect to perform at the Barclays Center in Brooklyn on July 11, a show that will start a long tour throughout the U.S. and continues through October.