"The referee will be embarrassed when he sees his decision not to give a penalty when James Harper fouled Keith Gillespie," Warnock said after the 2-1 defeat at The Madejski Stadium.
"As for being reported to the Football Association, you get used to these things - but it isn't me that should be reported.
"I don't understand why we don't have top-class referees for games like these.
"No disrespect to Grant Hegley, but there have been Premiership referees at nothing games in this league this season, so why not today when it was first against second?
"I told Grant that if he wants to go to the top as a referee, he will have to make tough decisions in front of crowds of 40,000 and 50,000 at Anfield and Old Trafford."