Amanda Nunes explains that she still wants a fight with Cris "Cyborg" Justino, but she needs more time to heal from a foot injury before doing so. (2:27)

Amanda Nunes says a right foot injury is what is delaying the biggest fight in women's MMA.

The UFC bantamweight champion appeared on Ariel Helwani's MMA Show on Monday and spoke of a pending showdown with featherweight champ Cris "Cyborg" Justino, saying, "This is definitely the fight that makes sense -- for me, for her, for the UFC."

Justino has proposed that the fight take place in September. Nunes wants it to happen in December. Sources told ESPN last week that the UFC favors the later timeline as well.

"We need some time to promote this fight," Nunes said.

That's not the only reason for the delay. Nunes revealed Monday that she suffered an unspecified right foot injury in her previous fight, a victory over Raquel Pennington in May.

"I still can't kick very well. I still can't run very well," Nunes told Helwani. "I'm better, but I still need time for therapy."

The promotion is hoping to match up the two titleholders in a featherweight championship fight at UFC 232 on Dec. 29 in Las Vegas, sources confirmed to ESPN last week.

Justino, who last fought in March, took to social media last week to try to persuade Nunes to fight her on Sept. 8. Later in the day, however, Nunes posted a photo of a signed bout agreement for the year-end card.

"That's six months away. I'm ready now," Justino said during an appearance on the same episode of Ariel Helwani's MMA Show. "She was calling me out in January. It's a long time. You cannot call out somebody -- 'I want to fight you' -- and make them wait one year until you're ready."

If the Nunes foot injury is an impediment, Justino added, she's willing to fight someone else in the meantime.

"I don't get paid for waiting," she said. "I get paid to fight."

The UFC has told her, however, that there simply are no other fight options for her. The women's featherweight roster bears this out. The UFC has just four 145-pounders in addition to Justino, three of whom (Holly Holm, Tonya Evinger, Yana Kunitskaya) she has already defeated. The other, Megan Anderson, lost to Holm in her only bout in the promotion.

But Justino believes it's personal. Ever since she was Ronda Rousey's biggest rival at the top of the women's game and company president Dana White publicly mocked her as "Wanderlei Silva in a dress and heels," Justino has not seen eye to eye with the UFC.

"Why are you going to punish me and make me wait one year in my prime?" she said. "If they make me wait until December to fight Amanda, probably it is going to be my last fight in the UFC."

Justino said her UFC contract expires in March.

"I want to fight, and my fans love to see me fight," she said. "The numbers do not lie."

Justino (20-1, 1 NC) is considered the best female fighter in the world, according to ESPN's pound-for-pound rankings. Her lone loss came in her professional debut in 2005, and most recently she defeated Kunitskaya in March via first-round TKO.

Nunes (16-4) is second in the ESPN pound-for-pound rankings. Her victory over Pennington in May was her seventh in a row, and she holds victories over Ronda Rousey, Miesha Tate and Valentina Shevchenko, among others.

Should she win, Nunes would become just the third fighter in UFC history to be a champion in two weight classes at the same time, joining Conor McGregor and Daniel Cormier.