Frontier Airlines is adamant they were NOT in the wrong when they booted UFC legend Khabib Nurmagomedov off a flight this weekend … claiming the 29-0 fighter ignored a flight attendant’s instructions before takeoff.

But, TMZ Sports just spoke to someone close to Khabib, who says that’s simply false.

First, Frontier’s side of things. The airline says Khabib — who was seated in an exit row — failed to indicate he was willing and able to assist in the event of an emergency.

Instead of kicking him off the plane, the attendant gave the retired fighter two options — switch seats or deplane.

The airline also added the video making rounds on social media failed to capture this part of the incident.

Frontier also made it clear the “decision to deplane the customer was in no way related to his ethnicity.”

We hit up Khabib’s manager, Ali Abdelaziz, who told us Frontier’s version of the story is fiction, adding his client insists he made it clear he was perfectly capable of helping if things went south.

“Lady who comes to me with questions was very rude from the very beginning, even though I speak very decent English and can understand everything and agreed to assist, she still insists on removing me from my seat. What was the base for that, racial, national or other one, I’m not sure,” Nurmagomedov explained on Sunday.

“But after 2 minutes of conversation, she called security and I was deplaned from this aircraft, after 1.5 hour I boarded another airline one and left to my destination. I did my best to stay calm and respectful as you can see on the video. But those crew members could do better next time and just be nice with clients.”