Ferguson, 34, was due to defend his interim lightweight title against Nurmagomedov in April, but injured his knee and was stripped of the belt.

Nurmagomedov, 30, became champion by beating Al Iaquinta and will make his first defence against McGregor.

"They took my belt, took a bunch of zeroes from my pay cheque," said Ferguson. "How do you think I feel?"

The American needed surgery after tearing his lateral collateral ligament a week before he was due to fight Russian Nurmagomedov.

He said: "I'm the champ. I didn't lose my belt, they took it from me. I've got a little bit of a chip on my shoulder. It's still there. It weighs a lot."

Ferguson will make his comeback when he fights Anthony Pettis on the undercard of McGregor-Nurmagomedov in Las Vegas.

Asked for his prediction for the big fight, he added: "Double knockout. I hope they knock each other out."

Ferguson says it is "in his contract" that he will step in as a late replacement if either McGregor or Nurmagomedov withdraw from the fight.