Conor McGregor and Khabib Nurmagovmedov have been warned by the UFC after their feud turned nasty.
The pair's rivalry has escalated on social media in recent days with McGregor aiming a racist slur at Nurmagomedov's wife.
The Dagestani responded by issues a warning of his own before UFC president Dana White stepped in.
He said in a statement: "I am aware of the recent social media exchange between Khabib Nurmagomedov and Conor McGregor. The ongoing situation has escalated to a level that is unacceptable.
"As such, we are taking the necessary steps to reach out to both athlete camps and this situation is being addressed by all parties internally."
Conor McGregor comes out of retirement 10 days after quitting
Both McGregor nor Nurmagomedov have been serving suspensions for an ugly brawl that erupted after their fight in Las Vegas last October.
The Irishman has since held negotiations about a summer return but refused to fight Donald Cerrone if their bout was not the main event.
White has also ruled out a trilogy fight between McGregor and Diaz.
The former two-weight champion 'retired' last week before appearing to reverse his decision on Thursday.
Earlier this week, White said he expected the Dubliner to return.
He said: "I think that there’s some things that Conor wants and I think that Conor wants to get together face to face, he and I, and we probably will in the next couple of weeks and we’ll get this thing figured out.
Conor McGregor breaks silence after 'racist' tweet aimed at Khabib's wife
"Listen, who gets respected more than Conor McGregor does? Come on, the guy’s never been disrespected, definitely not by me. And he’s got a lot of money too.
"But he’s stuck on this thing where he wants a piece of the ownership and that’s just - if you look at basketball, Michael Jordan didn’t own a piece of the league, and the list goes on and on.
"Is Conor very valuable to the sport and to the brand, the UFC? Of course he is. That’s a tough one, but I think there’s other ways that we can make him happy."
