Celtic manager Martin O'Neill fears defender Stanislav Varga may have suffered ligament damage in last night's friendly against Fulham.
The Slovak - who signed a new two year deal with the club this week - was stretchered off in agony just 18 minutes into the game at Loftus Road following a clash with Zesh Rehman.
Varga is likely to miss Celtic's trip to the United States where they will play friendlies against Manchester United and Boca Juniors. The squad fly out this afternoon.
O'Neill said last night: "It's hard to say yet but there is some swelling and our doctor . . . is very concerned. It's getting sore but we'll see how it is overnight".
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Celtic won the match 2-1.