The veteran rocker was performing with his group Further in Port Chester when he fell to the floor in the middle of a song, before exiting the stage and leaving his bandmates to play on without him.
Weir's bandmate Phil Lesh put the problems down to a shoulder injury, and the star was back on stage with the group for a gig in Atlantic City, New Jersey on Saturday (27Apr13).
However, the rockers have now cancelled a set at the BottleRock Napa Valley music festival in California as Weir is not well enough to perform.
A post on Further's Facebook.com page reads, "Due to unforeseen circumstances, Furthur regretfully will be unable to appear as scheduled at BottleRock Napa Valley (in California) on Thursday, May 9. Grateful Dead & Furthur co-founder Bob Weir, is unable to perform in any capacity for the next several weeks."
However, Weir still plans to hit the road for his solo shows next month (Jun13) and rejoin Further for the band's summer (13) tour, which kicks off in New York City on 11 July (13).