Chelsea midfielder Oriol Romeu is expected to be out for six months after undergoing surgery on Monday, the club has announced.
Romeu suffered a knee injury in the first half of the Blues' 3-1 win over Sunderland on the weekend, and missed the team's trip to Japan for the FIFA Club World Cup this week.
Following anterior cruciate reconstruction surgery and medial meniscus repair, Chelsea staff determined the 21-year-old would not likely return until next May.
Romeu has made 22 Premier League appearances since moving to Stamford Bridge from Barcelona in the summer of 2011.
George Saville, a 19-year-old midfielder who came up through the club's youth academy, has been added to the squad for the tournament in Japan.
Chelsea are also missing club captain John Terry through injury as they aim to win their first trophy and the control of interim manager Rafael Benitez.
The European champions' first match sees them face Mexican side Monterrey, the defending CONCACAF Champions League holders, in Yokohama on Thursday.
Information from the Press Association was used in this report.