The 37-year-old goalkeeper bizarrely aimed a karate kick at the back of Marc McNulty in the 89th minute of his side’s 1-0 win at Ibrox on Sunday – moments after brilliantly denying Florian Kamberi from close range.
It earned him a red card, ruling the veteran shot-stopper out of the final Old Firm derby of the season against Celtic next weekend.
Kris Boyd, his former Rangers team-mate, said of McGregor’s moment of madness: “It’s absolutely mental. I don’t know what he is thinking. It’s mental to even contemplate kicking out at someone.
“You can’t sit here and defend him. We have seen him have a couple of kick outs before. I’m lost for words.
“He is 36 now (sic) and not a silly little boy. It’s stupid.
“Rangers want to go and beat Celtic next week but now it looks like he’ll be suspended. It’s a crazy decision once again from him. He is a boy who lives on the edge and again it’s a moment of madness.”
Rangers boss Steven Gerrard refused to defend McGregor and admitted he was running out of ideas to tackle his squad’s discipline problems.
“I can’t defend it. He pulls a world-class save off to get us three important points and then he has a moment of madness where he loses control.
“It’s frustrating because we will miss our number-one keeper now and that will start with a very important game next week.
“It is frustrating, I should be going away thinking ‘we didn’t play well but it’s three good points, the run goes on’. But I’m not, I’m going away frustrated because I’m going to miss my keeper, who has been magnificent for me throughout the season.”
The red card was Rangers’ 12th of the season in all competitions. Alfredo Morelos’ first of five dismissals was later rescinded but both McGregor and Ryan Kent have had retrospective bans after red-card offences were missed on the day by match officials.
Gerrard – whose team triumphed courtesy of Jermain Defoe’s goal late in the first half – said: “I’m open to advice if anyone wants to give me any because I’m sure the players are sick of listening to me talking about discipline. It’s nine (league) red cards. That’s crazy.
“Our discipline problem is probably the reason why we are not talking about success and are talking about falling short, if you analyse it properly.
“This game is hard enough with 11. You need to be disciplined and keep your best players on the pitch.