Cardiff City boss Neil Warnock has slammed the head of the Professional Game Match Officials Limited Mike Riley, describing him as a "robot".

Warnock could face an FA charge for his post-match comments following a controversial 2-1 loss to Chelsea, which saw a number of decisions go against the Bluebirds.

Speaking ahead of Wednesday night's clash with Manchester City, Warnock continued his criticism of the English match officials.

"I always thought Mike Riley was a manufactured referee from day one," said Warnock. I don't think he's changed since then. He's been coached manufactured, almost like a robot.

"He knows everything about the rules, but I feel these people struggle to understand the game and the human element. A lot of referees are like Mike Riley and that's why I think we have gone backwards."