As per the report, McGregor has snapped his lower tibia and is expected to be sidelined for the foreseeable future.
It is the same injury suffered by Anderson Silva in July 2014 and which kept the former UFC middleweight champion out for nearly an entire year.
UFC president Dana White was not aware of the severity of the injury when he gave his press conference on Saturday.
“Lower tibia. The shin, I guess," White said at the UFC 264 post-fight press conference.
“I don’t know how the f--- they figured that out that quick.”
White also appeared open to the notion of having McGregor and Poirier meet for a fourth time after the fight, but he could not give a firm timescale on McGregor's return to the octagon.
“It’s all about timing, what’s going on, what’s happens since then,” he added.
“Conor goes into surgery tomorrow. We don’t know long how he’s going to be out. How much his rehab and therapy he’s going to need.”
SBG Ireland head coach John Kavanagh later revealed McGregor aggravated a pre-existing ankle injury during his preparations for his trilogy fight against Poirier at the T-Mobile Arena in Las Vegas.
“A little bit of that ankle injury had been aggravated during camp," Kavanagh said.
“We got a scan on it.
"Did that have a small part to play in weakening it? I don’t know.
"We were [with a doctor] a couple weeks ago to get a scan on the ankle. There might’ve been something in there.
"It would seem unusual that a young, healthy, fit man could wrap his foot around an elbow and [break it] without there being something [wrong] there before.
"You can play those guessing games all day long.”
Reacting to the injury, the coach said: “He throws a leg kick, and then he threw a teep. That’s clearly where the fracture happened.
"He threw an aggressive kick, Dustin shelled with the lead hand, and the foot wraps around the elbow in a similar fashion to [Anderson] Silva and [Chris] Weidman.
"They wrapped their foot around the shin, [McGregor] wrapped his shin around the elbow. He’s in the hospital right now. I’ll be heading over there after this to check in.
"It’s a bitter pill to swallow. This sport is the highest highs and the lowest lows. We’ve got to take some time to assess what the next move is.
"Obviously rehab and recovery is where it’s at.”
Kavanagh also came under fire from Michael Bisping after he defended McGregor's performance against Poirier in an interview with Laura Sanko on Sunday.
He added: “It was going fantastic. I thought he looked really, really good in there. I wasn’t concerned at all.
"I was actually really, really happy. At the 4:30 mark or even the 4:45 mark, everything is gravy. I thought energy looked good, technique looked good.
"A few adjustments in between rounds, and I thought round two we were well on track to getting a finish there, or keep the rhythm going for the rest of the fight.
“Credit to Dustin. He won. It’s an unfulfilling end to the night. It doesn’t feel properly finished. [There was no] closure.”News Now - Sport News