"Rowdy" Rousey, 26, has talked before about beating Velasquez, who is one of the strongest men in the world and arguably the greatest UFC heavyweight of all time. Rousey said that if given the opportunity, she could beat him in a fight.
"In any given moment, under the right circumstance, I think it is possible," said Rousey, the UFC women's bantamweight champion.
"You cannot tell me that it is physically impossible. It is possible that in any given moment, I could beat him.
"I always believe in my possibilities."
Rousey has had a good year for possibilities: Since January, she has debuted in the UFC, appeared on the cover of ESPN: The Magazine and cast in Fast & Furious 7 and The Expendables 3.
She is essentially undefeated since she started fighting, and was the first woman from the U.S. to medal in judo. She is credited with getting women featured in the UFC -- even changing the mind of UFC president Dana White, who had once said women would never fight in the organization.
With Velasquez weighing nearly 100 pounds more than she does, Rousey should have a hard time beating him.
But Rousey said she is married to her sport and plans to improve.
"My rivals think that they know what I'm going to do, but they don't. Every armbar in my fights is different, and has a different preparation.
"When a golfer hits a ball, they see the movement of the shot -- but they don't think about the swing, the move before. And there you have the key -- the first movement."