The club moved up five spots in the 2014 NFL Draft to select the wideout with the fourth overall pick out of the Clemson Tigers after impressing for three years in the college game.
After the first practice of training camp, Manuel is adamant that the Bills could have a star player on their hands.
He told NFL Network: "I don't know if you saw him out there, on a slant, stop on a dime - and he just turned the other way, on [Stephon] Gilmore, who I think could be an All-Pro corner and he made the play.
"The kid is special. I have thought that way since 2010."
Watkins recorded 101 receptions for 1,464 yards along with 12 touchdowns for the Tigers last season.