Nunez is expected to move on from Benfica in the upcoming transfer window due to serious interest from several clubs across Europe.
Manchester United have identified him as their top attacking target and have been working on a deal to sign the Uruguayan forward this summer.
Benfica are believed to be holding out for around €80m but there are suggestions that a deal could be done for as low as €60m once the negotiations reach their conclusion.
However, Vieira stressed that Benfica should resist selling him for anything less than his €150m clause just as he held out when Atletico Madrid signed Joao Felix in 2019.
He also insisted that Benfica should not sell him as there are other players they could easily cash in on this summer.
The former Benfica president told CMTV: “I was criticised so much for signing a player from the second division of Spain.
“When Joao Felix was sold, there were people at Benfica who said €60m or €70m, but he left for €120m.
“This one, if it was me, he would only leave for his €150m clause.
“I think Benfica should not sell him because he is essential for Benfica to be champions and there are others who could be sold.”
Nunez has prioritised moving to the Premier League with super agent Jorge Mendes tasked with the job of taking him to England.
