"Phenomenal," the rapper's newest single from the "Southpaw" soundtrack, debuted online on Tuesday.
"I am phenomenal / However long that it takes / I'll go to whatever lengths / It's gonna make me a monster though" he raps in the pump-up tune.
The "8 Mile" star was previously attached to play Gyllenhaal's character, down-on-his-luck boxer Billy Hope, but left the project in 2012.
Antoine Fuqua ("Training Day") directed the upcoming Weinstein Company release following the former boxing champion trying to make a comeback after losing his wife (Rachel McAdams), his career and daughter to protective services.
"Southpaw" hits theaters on July 24.