UFC on Fuel 7 will be live from London, England tomorrow morning.
Many fighters have plenty to gain with a win. Dustin Poirier and Cub Swanson could be fighting for a future featherweight title shot.
Other fighters like Che Mills and Jorge Santiago are fighting to prove that they belong in the UFC.
But the man with the most to gain will be Michael McDonald.
At just age 22, McDonald has already done more than many fighters will do their whole careers.
Currently he is on an eight-fight winning streak (15-1 overall). That includes knockout victories over former WEC champs Cole Escovedo and Miguel Torres.
McDonald would not only become a UFC champion with a win, he would become the youngest fighter to ever capture a UFC title.
Light heavyweight champ Jon Jones currently holds the record for youngest champion.
He was just a few months shy of 24 when he captured the light heavyweight title back in 2011.
What may make McDonald even more dangerous is his knockout power. He has four wins by submission, but is known more for his brutal KO's.
Although he is only fighting for an interim title thanks to Dominic Cruz still being on the shelf, McDonald could actually be facing a tougher task in Barao.
Barao comes into this bout on a 30-fight unbeaten streak. The only blemishes in his career are a loss in his debut and a no contest.
He's a great all around fighter who has defeated some of the best in the division, including Urijah Faber.
If McDonald can find a way to crack the Barao code, he will be the youngest fighter to gain a UFC title and just the second man to defeat Barao.