Neil Warnock has accused referees' chief Mike Riley of taking the standard of refereeing backwards in the Premier League.

Cardiff manager Warnock could yet receive a Football Association charge over his post-match comments about the officials following the controversial 2-1 Premier League defeat to Chelsea on Sunday.

But Warnock was defiant in his criticism of Riley, head of the Professional Game Match Officials Limited, ahead of Cardiff's visit to Manchester City on Wednesday.

"I always thought Mike Riley was a manufactured referee from day one," Warnock said. "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."