Reid had to be stretchered off at Bramall Lane after twisting his knee in a challenge with Sheffield United right back Tony McMahon.
The flying winger will have his knee assessed over the next twenty-four hours or so but first indications seem to unfortunately suggest that the injury could be relatively serious.
City assistant Steve Parkin confirmed: "He has twisted his knee when he's gone to receive the ball.
"Unfortunately for Kyel, his knee has got stuck in the ground and he said that he felt a sharp pain at the time.
"Matty (Barrass, club physio) knew straight away that Kyel would have to come off. He was in a lot of pain then and he unfortunately still is now.
"We can only wait and let things settle down now before seeing what the injury actually entails but certainly it looks quite serious.
"We've lost James Meredith recently to injury and it seems we may have lost another key player down our left hand side now. These players are not easy to replace but it looks like we might have to do that now.
"(Mark) Yeatesy himself has been suffering with a bit of a knee problem recently but it could be a chance for him now if Reidy is injured."