Gremio have confirmed Arthur Melo will move to Barcelona in January.
The two clubs have agreed on an option rising to €40m, which Barca are expected to trigger in July. A deadline for the clause runs to July 19.
Should Barca take up the option, Gremio say Arthur will stay until January 2019 on-loan before moving to Europe. They have insisted the midfielder must see out the championship in Brazil before leaving.
Arthur was likened to Barca captain Andres Iniesta by former Brazil coach Luiz Felipe Scolari last week.
