Lewis is helping Price train ahead of his rematch with Tony Thompson on Saturday and the former WBC, WBA, IBF and IBO champion thinks that the Liverpudlian is still some way off from a clash at the elite level.
"David is maybe eight, nine or 10 fights away from a world title," Lewis told the Liverpool Echo.
"He is still young and his frame is coming as he grows, and you grow into that, then your endurance becomes stronger and then your power becomes more.
"I would love to put some weight on him because he's slender and could definitely pack more pounds on because there are heavy guys out there. I think David needs to drink more Guinness."
Price will square off against Thompson at the Liverpool Echo Arena.