McMann's agent, Hector Castro of Empire Sports Management, confirmed her withdrawal from the fight, which was first reported by MMAJunkie.com.
Castro was unable to go into detail as to why McMann withdrew from the bout, but did say, “She will be back in the cage soon.”
The UFC is currently looking for a replacement to match up with Kaufman.
UFC Fight 27: Condit vs. Kampmann IIis slated for Aug. 28 at the Bankers Life Fieldhouse in Indianapolis. Carlos Condit and Martin Kampmann will rematch in the night’s main event on the new Fox Sports 1 network.
McMann, undefeated in seven professional bouts, made her Octagon debut by stopping Sheila Gaff by way of TKO in the first round of their bout at UFC 159 in April.
She was intending to be the one to welcome Kaufman to the UFC on Aug. 28.
Kaufman (15-2), like McMann, is considered one of the top women in the sport of MMA, and has been waiting a long time to make her promotional debut.
The Canadian fighter was the first Strikeforce women’s bantamweight champion, a designation she later lost to Marloes Coenen. She eventually fought her way back into contention, only to have Ronda Rousey submit her in the first round.
The Rousey bout was Kaufman’s final fight under the Strikeforce banner. She remained active this year, with the permission of UFC officials, by winning a decision over Leslie Smith at Invicta FC 5 in April.
Planning to face the former Olympic medalist, Kaufman is now left to wait and see if the UFC can line up a suitable replacement on just three weeks notice.