Hanson were forced to cancel their concert in Tulsa, Oklahoma on Wednesday (03Oct07) night after band member Isaac Hanson was hospitalised with a pulmonary embolism.
The trio of brothers had to call off their gig at the city's Cain's Ballroom venue after the 27-year-old was taken to hospital with shoulder and chest pains.
Isaac has suffered from the potentially lethal artery-blocking condition before.
The band's publicist Ken Philips says, "This could be serious, but nobody knows just yet. We are hoping for the best."
It is unclear whether Hanson will be able to play their next scheduled concert in Kansas City, Missouri on Friday (05Oct07).