The Scotland international had a campaign to forget last time out, with injuries restricting him to just 13 Premier League starts and a meagre return of three top-flight goals.
That followed an impressive debut season at the Stadium of Light, when the 27-year-old scored 11 times in 28 matches following a big-money move from Wolves.
But Poyet expects to see the best of Fletcher when the new term begins away to West Brom on August 16.
"I am really looking forward to seeing Fletch when the season starts," Poyet said in quotes reported by the Sunderland Echo.
"He's delighted. That's a big thing for a manager to have a player who is so happy at being fit and able to train every day.
"I have no doubt he'll return to form".
Poyet has spoken of his desire to add bodies to his squad, having already brought in the likes of Jordi Gomez, Billy Jones and Patrick van Aanholt.
