Svilar surpassed Iker Casillas to become the youngest goalkeeper in Champions League history when played against United at the age of at 18 years and 52 days last month in Lisbon.
Reports emerged earlier this week suggesting that Jose Mourinho had 'reserved' Svilar for United and it's understood that Sir Bobby Charlton spoke with Vieira after the side's match at Old Trafford.
"We have followed him since he was 15," Vieira told BTV when asked about Svilar.
"We've already had an offer for him, four times what we paid and where we would keep him for another two years.
"It's important to note, Svilar is 18 and only focused on Benfica. He won't leave."