Lee Wallace was taken off at half-time during QPR’s 1-1 draw against Watford because of an apparent stomach bug.
The defender felt ill before the game but believed he would be able to play.
However, he had to be replaced by Niko Hamalainen.
Boss Mark Warburton explained: “He was sick. He had a bad stomach before the game which we thought would calm down with medication.
“Unfortunately it got quite bad and he did well to get through the first half. Niko was ready.”
Rangers were without Rob Dickie, who will be assessed ahead of the trip to Rotherham.
Warburton indicated he was unsure whether Dickie would be able to play in Tuesday’s game after the defender “rolled his ankle” during training on Friday.