Ante Rebic scored the only goal of the game as Gabbia made a second-half cameo to replace the injured Simon Kjaer.
Pioli remarked: "Gabbia is a reliable player. He entered with the correct conviction. He deserves the satisfaction.
“When a player trains at this rate, it means he has important values."
Pioli also played down Mateo Mussachio's refusal to enter the pitch as Kjaer's substitute.
He added: “Musacchio had a pain in his calf and I was unable to call upon him. There is no case."