Shaun Wright-Phillips insists he is happy again at QPR after turning down "offers and opportunities" to move in January.
Blackburn goalkeeper Paul Robinson has told Sky Sports he will leave the club this summer and could move abroad.
The Greek outfit confirmed the capture - on a two-year contract - on their official website.
The 34-year-old former Barcelona full-back only signed a one-year contract extension at Monaco on Thursday after arriving in the principality the previous summer.
Abidal, who has won 21 titles including two Champions League winners' medals during a glittering career, recovered from a liver transplant in 2012 to resume playing for Barcelona.
The Frenchman, who has also played for Lille and Lyon, is Olympiakos's highest-profile signing of the close season so far as they look to build a squad capable of retaining their domestic crown and making a sustained challenge in the Champions League.