Light-heavyweight champion Jon Jones fights Chael Sonnen in the main event, and it's not clear at this point if McMann vs Gaff will be featured on the main card.
"I won't ever do things that are outside my character to gain followers," McMann said. "I won't fight in a way that people want to see. I'm going to fight in a way I think is great and true to me, which happens to be entertaining also. Competition is an extremely personal thing for me. I put my life into it. I won't be swayed at every turn by what fans and media want. I'm going to be me."
McMann is coming off a decision victory over Shayna Baszler at Invicta FC 2, while Gaff carries a three-fight win streak into her UFC debut.
Many expected McMann to fight Alexis Davis when both ladies were announced as new additions to the UFC's bantamweight roster, but it was not meant to be.
"I've actually become more aggressive since I've had my daughter," McMann said. "Before I had her, you couldn't really get me angry enough to be violent [outside of fights]. Now, if someone messes with her? I will hurt them."
No word yet on who Davis fights in her first UFC match.