'New Ronaldo' Joao Felix won't leave as Benfica target trophies - president
Attacking midfielder Felix, 19, is reported to have attracted the attention of top clubs including Real Madrid, Manchester United and Juventus.
He has scored 13 goals and set up eight in 22 league appearances since being promoted to the first team, but Vieira told the Benfica website that he would not be moving.
"In relation to our youngsters, mainly those that are today part of our main squad, Benfica will do everything so that no one leaves," he said.
"I can practically say and guarantee to Benfica fans that no one will leave. I'm one of the biggest mentors of this project and I will do everything within my power to ensure that no one leaves this year or next if possible."
Felix, who has a €120 million release, is under contract until 2023 and earlier this month became the youngest player to score a Europa League hat trick as Benfica beat Frankfurt 4-2 in Lisbon.
Defender Ruben Dias, 21, and winger Joao Filipe, 20, are also reported to be interesting a number of clubs, but Vieira said: "It's my conviction that Benfica can aspire to win a European title if it maintains its identity, and that is with players that have come from our youth teams.
"Every year we consolidate our project. There were four youngsters that came from our youth teams in our starting XI [for Monday's 6-0 league win over Maritimo] and I believe that it will be five, six or seven in the future."