Middlesbrough defender Rhys Williams is facing a lengthy spell on the sidelines after scans confirmed the Australian has damaged ankle ligaments.
The 24-year-old went down during the second half of Boro's Capital One Cup victory at Gillingham on Tuesday.
"He's had scans this morning and he's damaged his ankle ligaments," Middlesbrough boss Tony Mowbray told the club's official website.
"He will now see a specialist to decide if he needs an operation or not."
Mowbray has already reacted to the loss of the influential defender by bringing in former Reading and Burnley man Andre Amougou on trial.
Williams, who has scored five goals in 89 appearances for the Riverside club, has been capped 10 times by his country.