The Millers striker received his marching orders from referee Kevin Friend just after the hour after catching Leeds full-back Gaetano Berardi in an aerial challenge.
Although Berardi was left with blood streaming down his face, there was no intent from Derbyshire, who still received his first red card in English football and was forced to watch the rest of the game from the stands.
The dismissal looked like proving pivotal as the Millers, 1-0 up at the time, conceded 16 minutes later and were under the cosh as Leeds pushed for a winner, only for drama to unfold at the other end, with the hosts claiming a vital victory thanks to Greg Halford's penalty.
Boss Neil Warnock insists the challenge did not warrant a red card and his club will appeal the decision with the Football Association.
However, that cannot be lodged until Monday, with the verdict likely to be on Tuesday afternoon, so the Millers will prepare for their trip to Bristol City without Derbyshire.Ouch, that will sting in the morning #rufc pic.twitter.com/FLsup08c9d— Michael Marshall (@mickmarsh46) April 2, 2016
If Friend's decision is upheld Derbyshire will face a three-match ban which rules him out of the Ashton Gate clash, the visit to MK Dons and the hosting of Nottingham Forest.
Boss Warnock said: "I thought our sending off was
harsh, I’ve looked at it, we will appeal that.
"I don’t think he was going to
send him off until he has looked at him and seen the blood because he has gone
up with his arm.
"But Derbs isn’t like that, he hasn’t gone to elbow him so you
don’t know, it’s worth an appeal.
"It’s not a sending off but it will open the
door for someone else if he is suspended. Someone else will come in and score
the winner."
