Diario Nociticas reports Arsenal have struck an agreement with Porto over a potential move for midfielder Vieira.
It is claimed the 22-year-old will soon be an Arsenal player, although it's not clear as to whether or not that will have an impact on their pursuit of Youri Tielemans, who plans to leave Leicester City.
It was revealed last season that Liverpool had an option of first refusal on Vieira.
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