The centre-back, who joined the Millers on a free transfer in the summer, was carried off on a stretcher in the first-half of the League Two game against Northampton Town.
Andy Scott, the Rotherham manager, is braced to lose the centre-back for a lengthy period.
"He's not good. He just went to turn and his knee popped," he told Rotherham's official website.
"We'll have to let it settle down and get a scan but it doesn't sound good."