Conor McGregor has accused bitter rival Khabib Nurmagomedov of "chickening out" of his UFC lightweight title defence against Tony Ferguson later this month.

Nurmagomedov announced on Wednesday evening that he was back in his native Dagestan and ruled out the prospect of breaking the coronavirus quarantine to compete at UFC 249 on April 18 at a venue still to be decided.

UFC president Dana White has been at pains to insist the show will go ahead despite the global pandemic which has forced the event to be moved away from Brooklyn because of the partial US crackdown on the spread of the virus.

McGregor referenced the bizarre history of Nurmagomedov-Ferguson, with the two yet to meet in the octagon despite being booked to fight on five separate occasions since December 2015.

The previous four cancellations have been because of health or fitness concerns but McGregor, who had been linked with a fight against the winner, had no doubt who was to blame for the latest postponement.

"The fact of this matter is, both Tony and Khabib where engaged in a game of chicken here towards the fight bell," McGregor wrote on Twitter.

"With Khabib chickening out first. Making it 3-2 in pullouts in Tony's favour. Khab scurried out of the U.S to home, and amid the crisis. Very high risk. Congrats Tony."

The Irishman returned to the UFC in January by impressively stopping American veteran Donald Cerrone in his first bout since losing to Nurmagomedov in October 2018.

McGregor had planned to be more active in 2020 but admitted his relief he did not have a fight scheduled before the Covid-19 outbreak, as he believes he would have ignored the seriousness of the situation.

He added: "I am in shape to fight right now! At the beginning of all this, I said to myself – I'm happy I don't have an official fight booked.

"If I did, I would have consumed all the incorrect data to support me taking part in the bout, and I would have followed through, competed. And won."