Abidal endured a traumatic time at Barca as he was laid low by cancer, underwent a liver transplant and was later forced to leave when, having made an emotional comeback, the promise of a new contract never materialised.
The former France full-back joined Monaco last summer but has now moved to Olympiakos after a single season in Ligue 1 and was unveiled by the Greek champions on Monday.
Of his time at Camp Nou, the 34-year-old told the press: "I will never forget what my team-mates did for me [during my illness]. I don't think there has ever been anything like it."
Right-back Dani Alves offered to donate part of his liver to help Abidal return to a normal life, while former captain Carles Puyol let the Frenchman lift the Champions League trophy in his place when Barca beat Manchester United in the 2011 final at Wembley.
However, Abidal was also involved in a pay dispute with the Catalan club and left under a cloud after the public promise of a new deal was never fulfilled by the Blaugrana board.
"Despite everything, at Barca many other things happened that have never seen the light, that have never been published and that the press don't know about," he remarked, "and they are extraordinary things."
Abidal, who will link up with former Barca team-mate Ibrahim Afellay at Olympiakos, added: "I hope my experience and knowledge can help this club to grow. Wherever I play, I always give everything and my sweat will be proof of that."