It was only a matter of time before Conor McGregor piped up after Khabib Nurmagomedov’s victory over Dustin Poirier at Saturday’s UFC 242 event in Abu Dhabi.

The outspoken Irishman, who hit the headlines last month for punching an elderly man in a bar, hasn’t stepped inside the Octagon since his defeat to Khabib at UFC 229 last year.

But the 31-year-old had a keen eye on events in Abu Dhabi to see how his previous opponent would perform in his first fight since last October’s infamous scrap in Las Vegas.

Khabib further cemented his status as the best MMA fighter on the planet by retaining his UFC lightweight world title in style.

The Dagestani-born fighter was never really troubled by Poirier, who was submitted in the third round via a rear naked choke.

It was an emphatic performance from Khabib, who said: "I want to forget the bullsh** with the last guy (McGregor),” after his latest win. “Me and Justin Poirier have showed MMA is about respect not trash-talking.”

If McGregor was going to keep his mouth shut before, then he certainly wasn’t going to now.

A five-word tweet from The Notorious followed: “Book my rematch for Moscow”.

After what happened when you last faced Khabib - are you sure, Conor?

McGregor’s tweet has sparked plenty of negative comments from UFC fans, with many calling him deluded and, well, much worse.

But the harshest reply came from Justin Gaethje, a fellow UFC fighter who decided to give Conor both barrels.

Replying with the laughing emoji, the 30-year-old American added: “You’re a tool. You have lost everything already. You are a sh*t human, father, and husband. F**k you.”

Wow.

It’s unclear what McGregor has done to rub Gaethje (20-2 MMA) up the wrong way, but the Irishman’s response to that particular tweet will be interesting.

Perhaps Gaethje is eyeing up a potential bout with McGregor, who knows.

Whatever the reason, he may have gone a little too far here.

But Gaethje wasn't the only person who sent a brutal reply to McGregor...