McGregor (22-5), 32, of Dublin, Ireland, who was making his debut in the United Arab Emirates against Poirier, was caught napping several times by the American before he was eventually stopped in the second round.
While former UFC fighter Sonnen wouldn't quite go so far as to call McGregor a quitter per se, he did hint that the Irishman had quit on that occasion, as he feels he was essentially looking for an easy way out.
"There's a certain edge that certain fighters have," Sonnen said on his YouTube channel. "There's a certain anger and hostility that they bring to the ring.
"It's the very reason that they coined the phrase 'a rich man can't fight', because he's generally not angry, he's generally having a pretty good day, he doesn't have that edge.
"It's very relevant whether Conor finds it or not, because the Conor vs Poirier fight wasn't what you guys saw and the fans wouldn't understand this but every fighter did.
"That fight was over three minutes in, Conor was looking for the door, he just couldn't find it, but he was looking to get out of that fight.
"The reason every fighter can recognise it is that we have all done it, and we're all ashamed of it, but there's a look that a fighter has."
In the second round, Poirier landed numerous calf kicks on McGregor, crippling his right leg, which forced the referee to step in and wave off the fight - but Sonnen insists that wasn't the real issue.
In fact, as far as he is concerned, he feels that McGregor simply lost his nerve.
"There was a day when Conor McGregor, whether it was true or not, would never admit that a calf kick hurt, I will never say those words to you.
"You kicked me in a soft muscle in the back of my leg and therefore I lost an a-- whooping contest? You'd never get me to cop to it and there was a time when you'd have never got Conor to cop to it.
"There's this narrative around the fight about how good these calf kicks were, look, it's a weapon used by many, it isn't some great weapon."
McGregor is set for a rematch against Poirier in Las Vegas, and despite the Irishman's claims he will knock out his arch rival in front of a capacity crowd, Sonnen isn't convinced he will avenge his defeat.
He continued: "Conor found himself in a fight that was harder than Conor thought it was going to be against a guy whose a-- he had already whipped!
"Those are the things that started to play the mental game, and Conor thought 'land the big punch, let's make it look good and let's get out of here,' he went into panic mode.
"If you admit it ahead of time that panic mode and that fear, that adversity that you deal with loses its power, and I will be very curious as to what approach, from a media standpoint, Conor takes going into Poirier 3."News Now - Sport News