Local reporter Pedro Sepulveda is reporting Vieira, 22, is heading to London for a medical after Arsenal struck terms with Porto this week.
The versatile attacking midfielder has a release clause of £42million.
But Porto are accepting an initial offer of £30m plus add-ons.
And Vieira is now expected to become a Gunner as Mikel Arteta aims for a top four finish next term.
Sepulveda states the midfielder is now traveling to London for a medical and to complete the move.
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