Burnley captain Josh Cullen has been ruled out until late 2026 after sustaining an anterior cruciate ligament (ACL) injury in the 0-0 draw with Everton on Saturday.
He was substituted early in the second half at Turf Moor after a coming-together with Tim Iroegbunam .
Scans on Monday revealed the extent of the injury to his right knee, and the 29-year-old will undergo surgery and miss the rest of the season with his absence expected to be for around nine months.
Boss Scott Parker admitted the club may be forced into action in the January transfer window as a result.
"It's something we certainly need to look at," Parker said after Tuesday's 3-1 home defeat to Newcastle. "Josh is a huge loss for us.
"On the pitch he's probably been one of our best performers, so to lose him on the pitch as well as off, and what he gives us is a big loss."
Cullen, who will also miss the Republic of Ireland's World Cup qualifying play-off against the Czech Republic in March, started all 18 games of the season prior to Tuesday's match.
He was replaced by Florentino Luis against Everton and Parker added: "I thought the boys that came in, Luis and Lesley Ugochukwu , were very good but we'll look at it now over the coming weeks with the window opening and see where we may need to strengthen."
A club statement read: "Everyone at Burnley Football Club wishes Josh all the best for a successful and speedy recovery."
Burnley lost 3-1 at home to Newcastle on Tuesday in their first game without Cullen (REUTERS)
Burnley are 19th in the Premier League table on just 12 points, six behind 17th-placed Nottingham Forest , and have not won a top-flight game since a 3-2 victory over bottom side Wolves on 26 October.
Summer signing Quilindschy Hartman was not in Tuesday's matchday squad amid reports linking the 24-year-old with a swift return to the Eredivisie with Ajax.
However Parker said he expects the Netherlands full-back to still be with the Clarets at the end of the window and that it he was purely being given a breather.
"Just at the present moment in time we felt that 'Q' needs some air, needs some oxygen and we just feel it's best for him to be watching it from afar at this present moment," he said.
"It's been a whirlwind for him, coming from where he was, the injury and then coming into the Premier League and we just feel it's best for him to watch... I have no doubt that he will be here with us."
Additional reporting by PA
