Wanderers boss Dougie Freedman revealed the Bulgaria winger was in talks with the Barcelona-based club earlier this week and those talks have been concluded successfully.
The terms of the 33-year-old's transfer are undisclosed at present.
Petrov previously played in Spain for Atletico Madrid before his move to Manchester City in summer 2007.
He failed to nail down a regular starting berth during his third season with the Trotters despite scoring three goals in 16 appearances.
- Sports & Recreation
- Dougie Freedman
- Atletico Madrid