Newcastle captain Jamaal Lascelles has been ruled out for up to nine months after rupturing his anterior cruciate ligament during Saturday's win against West Ham.
Lascelles limped off with the knee injury in the 17th minute of Newcastle's 4-3 victory at St James' Park.
The 30-year-old defender has consulted a specialist and is expected to undergo surgery next week.
Lascelles' time-line to return will be between six and nine months in another hammer blow to Newcastle boss Eddie Howe.
In the midst of a troubled season, Howe was already without £250 million ($312 million) worth of talent due to injuries and suspensions for the win over West Ham, which saw Newcastle come from 3-1 down to snatch the points thanks to Harvey Barnes' late double.
"Newcastle United can confirm that club captain Jamaal Lascelles suffered a rupture to the ACL in his right knee during Saturday's victory over West Ham United," a statement from the Magpies said on Sunday.
"After seeing a specialist consultant, he is expected to undergo surgery next week and will be out for 6-9 months. Everyone at #NUFC extends their best wishes to Jamaal for a full and speedy recovery."
Lascelles has made 26 appearances for Newcastle in all competitions this season.
Earlier this month, he celebrated his 250th appearance for Newcastle and extended his stay at St James' Park until June 2025 after the club triggered a one-year contract extension.
AFP