Charlie Wyke could be out for two months after suffering a knee injury on Saturday.
The 25-year-old was only making his fourth appearance for the club after injuring the same knee shortly before arriving at the club from Bradford City in the summer.
Wyke was stretchered off after a challenge from Burton Albion goalkeeper Dimitar Evtimov and left the Pirelli Stadium on crutches.
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The striker has suffered medial ligament damage and is expected to be missing for six to eight weeks.
It puts significant pressure on Jack Ross's striking options, with Josh Maja and Jerome Sinclair his only other recognised centre-forwards.
He had hoped to add a versatile forward in the closing days of the transfer window but the failure to move on Papy Djilobodji and Didier Ndong meant that was not possible.
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After the Burton game Ross said it was 'frustrating' for Wyke.
"He is in a bit of pain, Charlie, we have to let it settle and assess where he is. It would certainly be a blow for us and the squad," he said.
"He has worked hard to come back, he has been playing catch-up. It would be even more frustrating if he had to start again in that sense."