Porto say they have agreed to sell midfielder Fabio Vieira to Arsenal in a 40m euro (£34.2m) deal.
The Portuguese club released a statement saying Arsenal would pay an initial 35m euros (£29.9m) for Vieira with the rest in potential add-ons.
Porto statement reads: “Deal complete for the amount of €40m, and of these, €5m are dependent on the achievement of sports objectives”.
Vieira, 22, has yet to win a senior cap for Portugal but was voted player of the tournament at last year’s European Under-21 Championship.
He provided 14 assists in the Primeira Liga last season.
Vieira also scored six goals in 27 league outings as he helped Porto claim the top-flight title in Portugal.
He has been capped 21 times by Portugal Under-21s and will become the Gunners’ third summer arrival, following USA goalkeeper Matt Turner and teenage Brazilian forward Marquinhos.
His versatility is extremely desirable as well as his ability to execute quality with both feet, a trait Mikel Arteta looks for in players as it opens up plenty of avenues when it comes to unpredictability and fluidity.
Vieira will likely feature in pre-season where his aim will be to develop chemistry with surrounding teammates and understand the requirements of the system in place so that he is ready when Premier League action resumes.