The Spain international moved back to the Nou Camp in the summer of 2011 in a £35m deal. But the agreement included a title-winning clause that stipulated Barca must pay another £2m once Fabregas had won his first La Liga medal.
Barcelona wrapped up the title after Real Madrid failed to beat Espanyol at the weekend. Tito Vilanova's side then went on to ease past Atletico Madrid 2-1 at the Vicente Calderon.
Arsenal also stand to gain in similar fashion from Hull City's promotion to the Premier League. Former-Gunners striker Jay Simpson has a similar clause in his Hull contract that entitles Arsenal to an undisclosed bonus - believed to be up to £500,000.
The extra cash injection could be put to good use this summer with Arsene Wenger linked with a number of players.
Cesc Fabregas himself has been mentioned as a possible target for Manchester United, but Arsenal have the first option on the Spaniard following his move to Barcelona.
Fabregas has failed to nail down a regular first-team place at the Nou Camp, and speculation has mounted linking him with a return to the Premier League.
But Barcelona are unlikely to want to lose a player they went to so much trouble to sign just two seasons ago.