Marrone made the announcement in a one-sentence release issued by the team Wednesday morning. Manuel is the Bills' first-round draft pick who has been recovering from a left knee injury sustained in a 20-16 preseason win over Minnesota on Aug. 16.
He missed two weeks before returning to practice on Sunday.
Marrone indicated he wanted to have his starter in place by practice Wednesday.
Had Manuel not been ready, the Bills would have turned to undrafted rookie Jeff Tuel to start.
Manuel, selected 16th overall out of Florida State, was the only quarterback taken in the first round of the draft.