Fulham midfielder George Williams will be out for around six months after rupturing his anterior cruciate ligament while on loan at MK Dons.
The 19-year-old Wales international sustained the injury during MK Dons' defeat by Chesterfield last week.
Williams, who was due to remain at Stadium MK until the end of the season, underwent surgery on Saturday.
He will miss Wales' crucial Euro 2016 qualifier against Israel in Haifa on 28 March.
The teenager, who extended his deal with Fulham until 2018 earlier this year, has won five international caps.