Jamie Lawrence could be out for two months after his cheekbone was fractured in a late-night incident.
The City midfielder definitely misses the home game with Ipswich and is due to see a specialist next week. If he needs an operation, Lawrence is unlikely to play until the end of March at the earliest.
It is a damaging blow for Nicky Law who had managed to hang on to the Jamaican international despite interest from Walsall.
It is understood the incident took place in Leeds following the 2-1 win at Grimsby last week. No other City players were involved.
Law said: "Jamie's got a triple fracture of the cheekbone. He's been to see the specialist and his opinion is that Jamie isn't fit to train or play.
"He will go back in a week's time when the specialist will re-assess it and decide if he will need an operation. If he does, and the bone needs plating, it will be a six to eight-week job.
"Jamie sustained that injury away from the football club but I can't go into it further than that.
"I'm just disappointed that having staved off Walsall I thought we had Jamie until the end of the season.
"We've only got two loans left, our resources are limited and everyone's doing their bit. That's what makes the injury to Jamie even more disappointing because it is not a football-related one."
Lawrence had been eagerly looking forward to facing Ipswich after the Walsall move failed to materialise.
He said: "All I want to do is concentrate on playing. The transfer talk didn't affect me."
The pitch is covered as City try to ensure they beat the freezing weather and stage the first home game since Boxing Day.
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