The Russian and Irishman have a longstanding feud and it was Khabib that had handed him a crushing defeat in 2018.
But after beating Donald Cerrone, retiring and then coming out of retirement, McGregor was back in the Octagon.
And Notorious was the overwhelming favourite to beat Poirier at UFC 257.
However, the American did not read the script and inflicted a shocking knockout in the second round.
Poirier upped the tempo after the duo traded blows and McGregor simply had no answer.
It left him crumpled in a heap on the floor before referee Herb Kean jumped in to call an end to the contest.
And Khabib tweeted after the clash: "This is what happened, when you change your team, leave the sparring partners who made you a champion and sparring with little kids, far away from reality."
It stokes the flames over a potential rematch, with UFC chief Dana White desperate for the two to meet in the Octagon again.
But it was reported that McGregor would have to put on a show to even tempt the Eagle out of retirement.
And that simply did not transpire, with the Dubliner looking off the mark - to which he admitted to.
In his post-match interview, McGregor admitted that a calf kick he suffered was the beginning of the end for him on Fight Island.
He said: "That low calf kick was very good, my leg was dead and I wasn't as comfortable as I wanted to be.
"Dustin is some fighter. I have to dust it off and come back and that is what I will do.
"I need activity guys come on, you don't get away with being inactive in this business. I'll take my licks, I am gutted man I put in so much work. It's a tough one to swallow.
"I would have liked to represent my team better but i'm gonna chill with my kids and that is it."