Chelsea will be without Ricardo Carvalho for at least four weeks after the Portugal defender damaged ankle ligaments in Wednesday's 5-0 win over Portsmouth, the Premier League club said on Thursday.
The London club, second in the league just one point behind champions Manchester United, were already depleted in defence with England left back Ashley Cole, Serbia defender Branislav Ivanovic and Carvalho's compatriot Jose Bosingwa all sidelined.
Chelsea's injury list also includes midfielder Michael Essien.
Carvalho will miss the April 3 showdown against United at Old Trafford but will hope to be fit to play for Portugal at the World Cup in South Africa starting in June.
Carvalho is the main stay of the Portuguese defence.
"The club will be able to determine over the next 24 hours whether the injury requires corrective surgery, however we can confirm at this point that he'll be out for at least four weeks," Chelsea said on their website (www.chelseafc.com).