19-year-old forward Felix has recorded an astonishing 10 goals and five assists for Benfica this season from just 18 appearances.
The teenager plays primarily just off the main striker but has shown the ability to play right across the forward line.
And Vieira believes that his performances, alongside fellow youngster Ruben Dias, validate the club's policy of investing in young talent, and hailed Felix's many qualities.
"There is only one sure thing: Felix is one of the best talents produced by Portuguese football after Ronaldo," Vieira told Tuttosport.
"He has an incredible technique, he is fast and also very intelligent.
"He is also a good person, he shows he has important values that make me very proud.
"Obviously I'm happy. Now it is clear that our project of betting on young people is bearing the desired results."
However, Vieira was adamant that there has been no official contact and that selling is not something the club are considering.
Juventus have also been linked with central defender Dias, 21, as their first-choice target as Matthijs de Ligt seems likely to follow team-mate Frenkie de Jong to Barcelona amidst fierce competition.
"You should ask [Juventus and Real Madrid if they are interested in Felix].
"We, at this moment, are not interested in selling and soon we will increase the figure of Felix's clause.
"It is neither the time nor the right occasion to talk about these things.
"It will be seen in the future. Ruben is 21 and in his role is one of the best in the world.
"He will have a brilliant career and I would like him to become our captain in the coming years."