The Catalan club stated that a further €10m will follow in variables for Arthur, who has signed a five-year deal.
Arthur, 23, will remain at Barcelona until the end of the season.
— FC Barcelona (@FCBarcelona) June 29, 2020
Miralem Pjanic will be going the other way in this unofficial swap deal where both operations are separate.
Since his arrival from Gremio for an initial €31m, Arthur has made 72 appearances for Barcelona.