Former Texas A&M Aggies quarterback Manziel is expected to be chosen high in the 2014 NFL Draft, with a number of experts predicting that he will be a top-10 pick.
A number of people have criticised both Manziel's size and attitude during the off-season, but ESPN reporter Gruden has declared that he thinks the youngster will become an excellent player.
He told CSN Chicago: "I realise he's under six feet tall but I think we blew that 'small' theory in the water last year with Russell Wilson and Drew Brees. I spent two days with him, and I know he can learn and he wants to learn.
"He had four different offensive coordinators and two head coaches at Texas A&M. It didn't matter; he adapted and did extremely well.
"The guy threw for 8,000 yards, ran for 2,000, and he had 93 touchdowns in two seasons. All I know is; I want him in my fantasy team."
Manziel has visited all of his potential future teams, but speculation remains as to whether the Houston Texans will choose a quarterback with their first overall pick.