Barao, who defeated Urijah Faber last July to earn the interim belt, stepped on the scale at 134 pounds, a number matched exactly by McDonald.
A win would make McDonald, who is just 22 years old, the youngest man ever to wear UFC gold. That designation is currently held by Jon Jones, who was 23 years old when he captured the undisputed light-heavyweight championship in March 2011.
McDonald though, will have to beat long odds, as Barao is considered a 3-to-1 favorite.
Both fighters bring long win streaks to the cage. Barao (29-1, 1 no contes) has won 19 fights in a row while McDonald (15-1) has captured seven straight. The winner could possibly face injured champion Dominick Cruz. The 27-year-old Cruz has not been able to fight since October 2011. Since then he has had two surgeries to address an injured knee. He hopes to return later this year.
In a key matchup between featherweight contenders, Cub Swanson will take a one-pound edge into the cage over Dustin Poirier. Swanson took the one-pound allowance allocated to non-title fights, weighing in at 146. Swanson, who has has had three straight knockout wins, is attempting to pad his resume in hopes of earning a title shot. Poirier has so far won five of his six UFC bouts.
All 24 fighters on the UFC on FUEL 7 card made weight. Full results are below.
Renan Barao (134) vs. Michael McDonald (134)
Dustin Poirier (145) vs. Cub Swanson (146)
Cyrille Diabate (206) vs. Jimi Manuwa (204)
Gunnar Nelson (169) vs. Jorge Santiago (170)
Ryan Jimmo (205) vs. James Te Huna (205)
Che Mills (170) vs. Matthew Riddle (170)
Terry Etim (155) vs. Renee Forte (156)
Danny Castillo (156) vs. Paul Sass (156)
Josh Grispi (144) vs. Andy Ogle (145)
Stanislav Nedkov (185) vs. Tom Watson (185)
Vaughan Lee (134) vs. Motonobu Tezuka (135)
Ulysses Gomez (126) vs. Phil Harris (125)