Gavin Williams is facing up to four months on the sidelines after suffering ankle ligament damage.
The Ipswich Town star was carried off on a stretcher during Sunday's pre-season friendly against Panathinaikos at Portman Road.
He was taken to hospital and an initial x-ray showed no bone damage, but he was due to have a scan once the swelling had gone down.
That took place yesterday with the outcome being a huge setback both for Town and Williams.
The Welsh international has ruptured his medial ligament and Blues physio Matt Byard said: "It's still very swollen and he will have physiotherapy to help reduce the soft tissue swelling.
"He'll be on crutches for a while and will be regularly monitored through his recovery period.
"It's difficult to be precise with a date for his return to full action, but at the moment we're looking at three to four months."
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