Mumford & Sons bass player Ted Dwane was taken to hospital yesterday, where doctors discovered a blood clot on his brain.
The band have postponed their next three shows in Dallas, Woodlands and New Orleans while he undergoes emergency treatment.
"Our friend and bandmate Ted has been feeling unwell for a few days, and yesterday he was taken to a hospital to receive emergency treatment," the band said in a statement.
"The scans revealed a blood clot on the surface of his brain that requires an operation. Ted is receiving excellent care and we are being assured that he will recover quickly from surgery.
"Sadly we have to postpone three upcoming headline shows planned for this week in Dallas on Tuesday [June 11], Woodlands on Wednesday [June 12], and New Orleans on Thursday [June 13].
"All dates will be rescheduled and will be announced as soon as we can; all tickets for this week's events will be honoured at their rescheduled dates.
"We have no plans to cancel or postpone any other appearances along this current tour. We're all wishing Ted a speedy recovery." (source)
