He expects rival clubs to test Stoke's determination to hang on to Faye, who cost £2.25m from Newcastle.
But Diao has reassured supporters that his countryman and friend is happy at the Britannia Stadium.
He told The Sentinel: "The first time the manager asked me about him, I said if he signed him, it would be his best signing for 10 years. Abdoulaye has proved that on the pitch and off it.
"If Stoke get good offers from other clubs then I think it will be difficult to keep him. But the good things is that he is happy at Stoke City.
"In fact, 'Happiness' is his new nickname at the club.
"The manager is a good man-manager and that makes a difference," added Diao. "He has given Abdoulaye a big responsibility as well as the captain's armband.
"That definitely seems to have brought the best out of him and City are benefiting."