Taking to social media, he shared a snap of himself with the MMA fighter.
“Rolling with the big dogs,” he captioned the image.
“Proper night out with The Don himself,” he added.
Another image showed the pair with dog breeder Colin Fitzpatrick.
It appears that they were enjoying a few drinks at Conor's Crumlin pub, The Black Forge Inn.
Earlier this month, the 23-year-old shared a snap of himself visiting the pub while posing with one of McGregor's most prized possessions.
In the picture, Casper, born Casey, holds McGregor’s UFC belt.
Casper and Conor, who appear to be pals for a few years, recently lost their mutual friend Darren ‘One Sup’ Nolan.
McGregor offered his condolences to the family of the viral video star who had found fame for both his freestyle rapping and his ability to down any large drink in one.
The UFC star left a heartfelt tribute on Instagram, alongside a photograph of himself and Darren's mum holding a framed photograph of the late viral star.
"I was late bro but everything for a reason,” he wrote.
“I will miss you Darren."
The Ballymun man died on December 9 of natural causes.
The young man’s funeral took place on Thursday morning.
Conor was also recently spotted partying at a friend's house after a video of him rapping and dancing emerged.
The clip, which reportedly took place inside a Dublin home, shows the UFC star side-stepping in a sitting room as he holds a can of beer and raps along to the music playing.
Wearing a grey t-shirt, grey tracksuit bottoms tucked into white socks, and white runners paired with a green cap, the Crumlin native is cheered on by some friends while he raps with another man dressed in all black.
Conor recently returned to training after breaking his leg in July during a match with Dustin Poirier.
He is eager to return to the octagon and recently requested a fight date with lightweight champion Charles Oliveira after the Brazilian submitted Poirer at UFC 269.
The Irishman tweeted a picture of himself wearing a UFC belt captioned: "So what date am I fighting Oliveira?” to which Oliveira responded: “What do you think about this weekend? I'm ready, I'm still in town, and there's an upcoming event. Let's go baby.”