McGregor was initially scheduled to fight UFC featherweight champion Jose Aldo, but the highly-anticipated match-up came to a disappointing end as Aldo pulled out with a rib injury.
As a result, McGregor will fight Mendes for the interim featherweight title, and the Irishman is already oozing confidence ahead of his fight on Saturday, so much so that he even tried to bet UFC president Dana White three million dollars that he would knock Mendes out in the second round.
During an episode of Beyond the Octagon on BT Sport in October last year, McGregor told Mendes that he would "rest my balls on your forehead". While some people may see this as nothing more than trash-talking, McGregor feels that he is intimidating his opponent and causing them to doubt themselves.
"The mental game is everything, not just in fighting but in most things," McGregor told reporters. "With a strong mind, you can take on anything. With a broken mind, you can take on nothing. It's definitely very important.
"Before the match would start, I'd be standing on the side where the ball was going to be kicked into play. And I'd get into the guy’s face a little bit, try to (mess) with his head so he'd play scared."