"Barcelona are the ones who asked to bring my transfer forward this summer. It's a question of the clubs. My departure has been transparent and I'm very happy with how it has gone. It has been good for everyone involved," he told a news conference.
Barcelona announced the deal to sign 21-year-old Arthur for 30 million euros (£26.5 million) plus nine million in variables back in March, revealing they could activate it as of July 2018.
The player, however, was not expected to move to the Catalan club until January 2019.
Barca did not respond to requests for comment, although reports in the Spanish media said the move would be made official next week.
Arthur helped Gremio win the Copa Libertadores last year and has been signed to help fill the void in the Barca midfielder vacated by Andres Iniesta, who ended a 16-year, trophy-filled period at the club in May to sign for Japanese side Vissel Kobe.
Arthur's transfer is also thought to have been brought forward due to midfielder Carles Alena suffering a serious knee injury in the Barca reserve side's final game of the season.
(Reporting by Richard Martin; editing by Ken Ferris)
