The quarterback underwent minor surgery on a knee injury and will miss the Bills' remaining pre-season game against the Detroit Lions.
When asked if Manuel would be fit for their season opener, Marrone told the club's official website: "That's what I'm hoping for. He had the procedure done and he was with us on the field the other day just watching and observing.
"I think we just have to wait until that period where the doctor looks at him and says, 'Here's where we are.'"
Buffalo begin their regular season campaign against the New England Patriots on September 8.