Hull City's David Livermore fears John Welsh broke his leg in the 2-0 win over Preston.
Welsh lasted just five minutes against The Lilywhites after attempting to tackle Neil Mellor, before being replaced by Livermore.
Preston boss Paul Simpson felt Welsh should have been dismissed, but the ex-Leeds man thought it was a 50-50 challenge.
"It looks like he has broken his leg and he is an important player for us," he said. "But to me, it looked like a 50-50 challenge.
"John's gone in hard, their player has gone in hard, but John's come out of it worst. I don't understand why they were upset because it was a 50-50 tackle.
"It was a surprise to get on so early but all you can do is get on with it and take your chance."