Montano was transported to a hospital before the weigh-in as a "precautionary measure" and due to "health concerns," according to the UFC. Neither she nor Shevchenko fought on the card.
The fight was supposed to co-headline UFC 228 at American Airlines Center in Dallas.
In a statement posted late Saturday night on her Instagram account, Montano said she felt being stripped of her belt was "uncalled for."
"There have been plenty other fighters who have not been punished for a lot more," she wrote. "Unfortunately I'm not one to be running my mouth, so I don't bring in the big bucks."
In the post, Montano wrote that she experienced issues with her kidneys as well as "an imbalance of electrolytes" and high sodium levels.
Montano (4-2) became UFC's first female flyweight champion in December but has not defended her title yet due to health reasons. She has battled a foot injury and had her tonsils removed in 2018.
Shevchenko (15-3) has been waiting for a shot at the 125-pound title and was heavily favored to defeat Montano on Saturday. During the past two months, she repeatedly said she was not confident Montano would ultimately face her.
Shevchenko posted to Instagram on Friday, saying she believed Montano plotted to "escape from the fight the last minutes."
View this post on Instagram
I am not surprised about this situation with Nicco. And I told it before, she can pull out from the fight at anytime. She was trying to avoid this fight several times already. It is my 3rd preparation for this fight. Looks like It was her plan from the beginning, to show up for the fight week , to build up her name, speak confident and secure, and then escape from the fight in the last minutes. She was speaking about Fighting spirit and character.... What kind of fighting spirit she is talking about? I don't believe in a version about health issues, she was looking totally fine in open work out and media day. Her actions are totally unprofessional! First of all I am very sorry for all my fans who came to support me! I am very upset about all this happening. I was preparing for this fight hard and serious. My plan was to leave Dallas with the belt. I will keep moving forward. And will seize the next opportunity to take what is mine. Thank you everyone of my dear friends for your support!
Montano responded to Shevchenko in her post late Saturday night.
"Never have I ever experienced working with an opponent who is so heartless and disrespectful," Montano wrote. "You can absolutely guarantee I'm coming back to make my stamp and take back my belt!"
UFC has not stated whether the fight will be rescheduled.
Information from ESPN's Ariel Helwani was used in this report.