Chart-topping English indie folk rock band Mumford and Sons postponed three sell-out shows on their US tour Tuesday while bassist Ted Dwane undergoes surgery for a blood clot.

Writing on its website, the group -- winners of this year's Grammy for best album -- said scans had revealed a blood clot on the surface of Dwane's brain that requires immediate treatment.

"Ted is receiving excellent care and we are being assured that he will recover quickly from surgery," it said without disclosing where the operation will take place.

Dwane, who plays upright bass, turns 29 on August 15.

In the interim, Mumford and Sons is postponing headlining concerts this week in Dallas and Woodlands, Texas and in New Orleans, Louisiana. Tickets will be honored at rescheduled dates.

"We have no plans to cancel or postpone any other appearances along this current tour," said the band, which is lined up to play the Lollapalooza festival in Chicago on August 3.

Mumford and Sons have been at the forefront of a folk and bluegrass revival that also includes The Lumineers from Colorado. Its latest album "Babel" entered the British and US charts at number one upon its release in September.