Newcastle defender Kieran Trippier faces a race to return before the end of the season after having surgery on his broken foot just weeks after joining the club.
The England right-back fractured a metatarsal bone in his left foot during Sunday's 1-0 win against Aston Villa in the Premier League.
The 31-year-old has played a key role in Newcastle's climb out of the relegation zone since his £12 million ($16 million) move from Atletico Madrid in January.
Newcastle manager Eddie Howe said Trippier, who joined the club with a clutch of other players during last month's transfer window, had the operation on Thursday, but his return date remains uncertain.
"He had his operation yesterday and that went well, so that was good news," he said on Friday. "I don't know at this moment in time how long he's going to be out.
"We hope to have him back before the end of the season but it's obviously a significant injury, which is a big blow to us because he was performing so well."
Trippier had scored in each of his past two league games, with Newcastle winning three in a row to move four points clear of the bottom three.
Howe acknowledged the former Tottenham star's absence would be a major blow for Newcastle as they look to preserve their top-flight status under their new Saudi-led ownership.
Although Trippier will not be able to make an impact on the pitch for a while, Howe hopes the defender can still help out with his infectious leadership.
"That's the type of person that he is -- he wants to make a difference, he wants to help and he wants to lead, so he'll have a big impact even if he's not playing," said the Newcastle boss.
"Straight away (after the game), just his reaction to that wasn't one of head down, he didn't take himself away in isolation, he was very positive. He was around the players and giving off good energy, and that's been him since day one here.
"The energy and positivity around him is infectious and it's definitely affected the people he's been around, hence a really positive reaction from the squad."