Kurt Zouma will this week undergo knee surgery which will rule him out for the rest of the season and Euro 2016, Chelsea have announced.
The France defender injured his anterior cruciate ligament in Sunday's 1-1 Premier League draw with Manchester United.
A statement on Chelsea's official webiste read: "Kurt will undergo surgery in the next 48 hours and is expected to be out for approximately six months."
Zouma landed awkwardly early in the second half of the drawn Premier League contest and was taken off on a stretcher.
He vowed to return "stronger."
Zouma has started 16 of the last 19 Chelsea matches in all competitions, displacing Gary Cahill as first-choice alongside captain John Terry.
Cahill, the England vice-captain, will welcome the opportunity to return to the starting XI, even if the circumstances are unfortunate for a team-mate.
Spain full-back Cesar Azpilicueta told the Evening Standard: "Gary is one of the veterans of the team. We know his quality and in this squad, it is always important to be ready.
"We need everybody, we have big games coming up and all of us have to be ready."
Cahill will likely line-up alongside captain John Terry in Saturday's Premier League clash with Newcastle.