Ole Gunnar Solskjaer labelled Nemanja Matic's dismissal a 'joke' following Manchester United's Carabao Cup semi-final defeat by Manchester City.
Matic was sent off in the second half for a second yellow card when he blocked City's Ilkay Gundogan.
The Serbian midfielder, who had put United back into the tie after scoring in the first half, received his first booking when he fouled Riyad Mahrez.
Solskjaer felt referee Kevin Friend and his fellow officials had made the wrong call in sending him off.