Newcastle defenders Jetro Willems and Paul Dummett will miss the rest of the season, manager Steve Bruce has confirmed.
A scan has shown loan signing Willems ruptured his anterior cruciate ligament in Saturday's win over Chelsea, while Dummett could face surgery on a tendon injury.
"We've been unfortunate," said Bruce, whose side play Everton on Tuesday.
"We may have to change our transfer plans too."
Bruce is hopeful of clinching a loan deal for Inter Milan winger Valentino Lazaro but says losing two left-sided defenders is a blow.
"Matt Ritchie played there on Saturday but he's only just back after four months," he said.
"It's unfortunate because Jetro was settling in well and adapting to life in the Premier League. He's been a very decent player for us, so we'll miss him."
Newcastle have had bad luck with injuries this season, suffering nine over the Christmas period, but sit 12th in the Premier League.
After Everton on Tuesday, they play Oxford United in the FA Cup fourth round on Saturday.