Portsmouth fear Lassana Diarra could be out for three weeks - but will not know until he returns from international duty with France.
The £5.5million midfielder limped off after just 19 minutes of Saturday's goalless draw at West Ham in the Barclays Premier League, after taking the full weight of Scott Parker's mistimed challenge on his right ankle.
Pompey boss Tony Adams explained: "Lassana is our most influential player and has turned his ankle. I'm not a physio, but in my experience you are looking at weeks out when you do something like that."
Adams knows the playmaker is almost certain to miss Saturday's home game with Hull and next Thursday's UEFA Cup clash with AC Milan. France demanded Diarra's presence for their home friendly with Uruguay on Wednesday night - despite the injury.
The player is being treated by the international side's medical team following a scan and will not return to his club until Thursday.
"At a club like Portsmouth injuries like this have an effect," Adams added. "We lost Sol Campbell and Niko Kranjcar with injuries before the West Ham game and we haven't got the luxury like the big teams of having a massive squad."
Adams admitted he was upset that Diarra could not remain in England to be treated by Pompey's medical staff.
He continued: "I've still had to let him go away and travel to France. I didn't want him on a plane when his ankle is going to blow up.
"I would like to have scanned him on Sunday and then given them a fair assessment but now we have to wait."
Adams hopes captain Campbell (toe) and winger Kranjcar (ankle) may be available to face Hull at Fratton Park on Saturday.
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