The UFC's planned return to action May 9 will have to be without one of its top champions.
Nunes first mentioned the news to CBS Sports in an interview published Monday, saying the date was too soon given the coronavirus pandemic.
"I don't think this is the right time for me right now to fight," Nunes said. "Let this coronavirus pass a little bit so I can at least have a full camp. We can maybe see around June, [but] let's see what is going to happen."
Nunes, the pound-for-pound top women's MMA fighter in the world, is also the UFC's women's bantamweight champion. She said she has not been able to have a full training camp due to the pandemic. Lambert added that Nunes had a small injury that wasn't fully healed when she started her training, and she needs more time.
Spencer told ESPN that she was told by the UFC to be ready for June, so that is what she plans on doing. She will not remain on the May 9 card.
Nunes said it has been hard to get top-level training in due to American Top Team, where she trains in Coconut Creek, Florida, being open only to athletes who have upcoming bouts.
"It's not many people, just me and a couple guys that are going to be on the same card as me," Nunes said. "We all have separate training with just me and my coach, one on one. I keep in shape like that. I go to the gym only one time in the morning and do everything. I do a couple of things by myself and some things that I need a coach. Then I come home, and I really do everything I need to keep in shape. I have a treadmill and some weights."
Nunes (19-4) has won 10 straight with five successful bantamweight title defenses. "The Lioness" is the first woman in UFC history to win titles in two different weight classes.
Nunes, 31, has the most wins (12) and most title-fight wins (7) among women in UFC history. A Brazil native, Nunes has not lost since 2014 and won the featherweight title by knocking out Cris Cyborg at UFC 232 in December 2018.
Spencer (8-1) has just one career loss, to Cyborg at UFC 240 in July 2019. Spencer, of Canada, lives and trains in Florida and is coming off a first-round TKO win over Zarah Fairn dos Santos in February. Spencer, 29, is the former Invicta FC women's featherweight champion.