Arsenal midfielder Alexander Hleb was undergoing a medical at Barcelona on Wednesday ahead of an £11.9m move to the Nou Camp.
Barcelona confirmed the deal for the 27-year-old Belarussian and he arrives as Ronaldinho travels to Italy for a medical at AC Milan.
Hleb had been linked with Inter Milan, but Barcelona have won the race.
Arsenal have also lost Matthieu Flamini to AC Milan and Gilberto Silva is poised to sign for Panathinaikos.
606: DEBATE
How will Wenger cover Hleb's departure?
Barcelona have announced that Hleb will have medical tests throughout Wednesday and is expected to sign a contract on Thursday.
Barcelona vice-president Marc Ingla confirmed in June that they were in talks to sign Hleb, saying: "Barcelona's negotiations with Hleb are still in progress.
"But despite him being a player with special qualities, if his club are not ready to sell him, we have other options in mind."
Hleb's departure from the Emirates Stadium has seemed likely all summer after the player admitted he was "mentally tired" of the combination of living in London and playing top-level football.
He joined Arsenal in 2005 after the club paid Stuttgart £11.2m for his services, and if he signs he will become Barcelona's fifth summer signing following the arrivals of Seydou Keita, Gerard Pique, Martin Caceres and Daniel Alves.
