Boxer Floyd Mayweather can be open to a fight with Khabib Nurmagomedov after he has responded to the challenge of the UFC hunter by saying: "Get the checkbook out!"
On Sunday, 30-year-old Russian American Mayweather, who is also undefeated, adds: "In the jungle there is only one king."
Mayweather, 41, defeated Conor McGregor in a boxing bout in August 2017.
The return of the Irishman to UFC ended on 6 October in the defeat of Nurmagomedov.
That extended Nurmagomedov's unbeaten mixed martial arts record to 27-0.
Former five-weight world champion Mayweather, who is unbeaten in 50 fights, said on Twitter: "CBS, Showtime and MGM Grand get the checkbook!"
It came after Nurmagomedov, in a video on Instagram filmed with Leonard Ellerbe, the chief executive of Mayweather Promotions, said: "Let's go, Floyd, we have to fight now,
"50-0 v 27-0 – two boys who never lose, why not?"
Nurmagomedov, known for his wrestling skills, caught McGregor with a bang before winning his match with a choke while forcing his opponent to tapping.
Mayweather stopped McGregor in the 10th round in their fight, one of the richest bouts in the boxing history.
"Of course I am the king because he could not drop McGregor and I let him fall easily," added Nurmagomedov, who retained his UFC lightweight title against McGregor.
Mayweather, who has not fought since the McGregor contest, said he will come out of retirement to fight Manny Pacquiao in a rematch later this year.
Nurmagomedov and McGregor were both temporarily suspended by the Nevada Athletic Commission in anticipation of a full investigation into the scenes that marred the end of their battles in Las Vegas.
After his victory, Nurmagomedov jumped on the octagonal fence and began to fight the team of his rival. McGregor then fought with the Russian's camp because a lot of fights broke out.