Koscielny joined the Gunners from Lorient in the summer of 2010, but did not benefit from a high-profile in England.
"He gave me a chance to play for a big club like Arsenal," said Koscielny.
"He took the risk to buy me from a small club like Lorient, he shaped me, and helped me grow as a player and as a man.
"I think he won his bet."
The Frenchman added: "Every weekend I try to prove that he was right to trust me for this club. I try to do my best on the pitch.
"I'm not the only example - there have been plenty during these 20 years at arsenal. That's the work he's done over all these years."