Manganiello will portray the leader of a private military group, while Shelton will play a scientist and astronaut, according to The Hollywood Reporter.
Brad Peyton is directing the movie, which reunites Johnson, Peyton and producer Beau Flynn, the team behind "San Andreas" and "Journey 2: The Mysterious Island",
Johnson will play an animal-loving hero who is the world's only hope, while Naomie Harris, who is already on the call sheet for the monster movie, will essay the role of geneticist with a moral streak.