Charlton Athletic midfielder Jonny Williams will be out for at least two months with a knee injury.
The 26-year-old Wales international suffered the injury during the first half of Saturday's 3-0 win over Derby.
Williams, who has made 12 appearances for the south-east London side in the Championship this season, had an operation on Tuesday.
"It is disappointing because he has been doing well for us and flying," boss Lee Bowyer told BBC Radio London.
"It is minimum eight weeks and then we have to get him fit."
Williams started both of Wales' recent Euro 2020 qualifiers against Slovakia and Croatia, and his absence from next month's crucial final two games against Azerbaijan and Hungary will be a blow for manager Ryan Giggs.
Meanwhile, Bowyer says the prognosis for Sam Field is "not looking good" after the on-loan West Bromwich Albion midfielder was stretchered off during the 2-1 defeat at Bristol City on Wednesday, while Jake Forster-Caskey will be out for "a few weeks" with a hamstring injury sustained in the same match.
"We are rapidly running out of numbers," Bowyer added.
"It is tough for us and we can't get a break at the minute. But we will keep battling on."