The Black Cats succumbed to a 2-1 defeat to Chelsea in the Italian's first game in charge of his new side.
Gardner told the club's official website: "The boss has been brilliant since coming in. He knows what he wants from his players and he really studies the game inside out.
"He makes his players feel that they are the best and that's what you want from a manager."
Sunderland face Newcastle United in the Tyne-Wear derby next week as their fight against the drop from the Premier League continues.