Chelsea defender Ricardo Carvalho is facing at least four weeks on the sidelines and could require surgery on damaged ankle ligaments.
The Portugal international suffered the injury in the first half of Wednesday night's 5-0 victory over Portsmouth at Fratton Park.
Centre-back Carvalho limped off the field in the 37th minute following a challenge with Aaron Mokoena, with burly Brazilian Alex taking his place alongside John Terry.
The former Porto player will now miss several key fixtures for the Blues as they chase Premier League and FA Cup glory.
Carlo Ancelotti will be without the talented defender for the crucial Premier League meetings with Aston Villa and Manchester United on the next two Saturdays.
Carvalho will also be absent when the Stamford Bridge side travel to Wembley on 10th April to tackle Villa in the FA Cup semi-final.
And he could be forced to go under the knife in a bid to cure the problem, with the club waiting to discover if an operation is needed, which could put his World Cup hopes in jeopardy.
A statement on the club's official website read: "Chelsea can confirm that Ricardo Carvalho suffered ankle ligament damage in last night's game against Portsmouth.
"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 moved back to within one point of leaders United with Wednesday's thumping victory, while London rivals Arsenal are just one point further back in third.
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