Ronaldinho was granted dual nationality by Spain on Monday, the Spanish Primera Liga club said.
The move frees up a place for another non-European Union player in Frank Rijkaard's squad.
Mexican forward Giovani dos Santos is set to take up the vacant slot alongside Cameroon international Samuel Eto'o and Ivory Coast midfielder Yaya Toure in the non-EU berths permitted under Spanish Football Federation (RFEF) rules.
However, Dos Santos is also expected to be granted dual nationality this week.
Barcelona opened their league campaign with a goalless draw away to Racing Santander on Sunday.