Middlesbrough skipper Rhys Williams is expected to be sidelined for up to four months after undergoing ankle surgery.
The 24-year-old Australia international had an operation to repair damaged ligaments in London on Monday and has now started the lengthy rehabilitation process.
A club spokesman said: "(Williams) underwent a successful operation in London on Monday and his rehabilitation is now underway.
"However, he is expected to be out for the next three to four months."
Williams suffered the injury during Boro's 2-0 Capital One Cup second-round victory at Gillingham on August 28.