Rotherham are bracing themselves to be without Michael Raynes for some time after he was stretchered off against Northampton.
The defender, a summer signing from Scunthorpe, was replaced by Luke Foster midway through the first half having gone down clutching his knee.
"He's not good," boss Andy Scott told Millers Player after the game. "He just went to turn and his knee popped.
"We'll have to let it settle down and get a scan but it doesn't sound good."