The winger was believed to be a target for Liverpool manager Jurgen Klopp, but the Blues have moved quickly to beat their Premier League rivals.
Brahimi contributed with more than 20 goals plus assists last season and managed to impress in the Champions League.
According to latest reports, Chelsea are in the final stages of negotiations for the Porto winger and a deal should be completed soon. Initially Porto wanted to sell him for a sum of 30 million Euros, but due to FFP pressure, they are now looking to sell him for half the price.