The 21-year-old had anterior cruciate reconstruction surgery and medial meniscus repair on Monday after being forced off in the first half of Saturday's 3-1 win against Sunderland at the Stadium of Light.
Romeu lasted just 20 minutes on Wearside before being replaced by Oscar. It was hoped the former Barcelona man would be fit enough to fly to Japan with rest of the squad to take part in the Club World Cup.
|ONE STEP FROM SILVERWARE|
|15/2||Chelsea are 15/2 with bet365 to beat Monterrey 2-1 on Thursday in the Club World Cup|
Romeu has appeared nine times for the Blues this season, scoring once in the Capital One Cup thrashing of Wolves at Stamford Bridge in September, and has racked up 33 games overall since arriving from Barcelona in 2011.