Richard Keys has suggested there could be a bias from the officials during Wednesday night's Manchester derby.
United and City meet at Old Trafford with the clash likely to go a long way to deciding the Premier League title.
The clash with their fiercest rivals is City's toughest in the run-in, with Liverpool fans hoping they slip up.
Ahead of the clash, former Sky Sports chief Keys has claimed official Scott Ledger is a Liverpool fan - and should not be on the line at Old Trafford.
"I can’t see why anything should go wrong. Officials always call a decision as they see it - but why is Scott Ledger - a Liverpool fan - running the line tonight?" he asked on Twitter .
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"Who makes these decisions? Are we short of assistants? Imagine. Just imagine...."
Ledger was temporarily taken off Premier League duty in 2016 after awarding a controversial penalty to Liverpool in their clash with Crystal Palace .
Andre Marriner will be the man in the middle at Old Trafford, with Ledger and Simon Long his assistants.
Craig Pawson has been named as the fourth official.
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Speaking ahead of the clash, Ole Gunnar Solskjaer put pressure on the officials over City's tactics to give away fouls high up the pitch.
"You don’t get the yellow cards [there], do you? But that’s just because they commit so many players forward and you can clearly see that they’ve got them in that mould of trying to win the ball back, and they do make fouls," he said.
"It's up to us to play through that press, be ready enough, play one- and two-touch, don’t give them time. It’s not my decision, it’s the referee’s responsibility to do that.”
An unimpressed Guardiola responded: "I don’t like it. No. My team is not built to think and create for that, not at all."
