Saliba has signed for the Gunners, but will play this new season on-loan with ASSE.
Sanllehi said, "We are delighted with this loan because the level of intensity and demand is very strong in the Premier League.
"William Saliba is probably still a bit young to play right now. We must protect this young talent. We think it is good for him to continue his training in a less demanding championship, we will then have a top defender for a decade.
"He realised that this loan is the perfect solution for the evolution of his career."