The 22-year-old scored 7 times while registering a further 16 assists for Porto last season, emerging as their leading creative outlet following the January departure of Luis Diaz to Liverpool.
It proved a breakout campaign for Vieira, who had only made his first-team debut in June 2020 before imposing himself on first-team proceedings from December onwards.
Former West Ham defender and Portugal international Jose Fonte urged supporters to get “very excited” about Vieira’s arrival and compatriot Fernandes backed up those claims.
Speaking to reporters in Portugal, the Manchester United star said: “I welcome all Portuguese players who go abroad, I hope he can shine to the fullest, except against me.
“Fábio has a lot of quality and has been demonstrating that, whether in the FC Porto is in the Under-21s, he has had good numbers and good performances.
“I hope he succeeds like all the Portuguese out there. We have to start valuing what is ours and I hope that Fábio manages to be as good as possible, despite of wanting to stay ahead.”
Arsenal are expected to seal a £45m deal for Gabriel Jesus imminently while the club continue to chase a move for Ajax defender Lisandro Martinez.