The 24-year-old struggled for form during his first season with the Black Cats last term, which had resulted in reports that he could depart the Stadium of Light.
However, Poyet has insisted that the USA international is "really happy" on Wearside, despite having competition for his place in the starting lineup.
"The idea is always to have options. We talk about Fletch (Steven Fletcher) and Connor [Wickham], but I can say that I've never seen Jozy as happy as now," Poyet told the Sunderland Echo. "I've got no explanation for that. But he looks really happy and knows everything that is going to happen and why.
"I think last year, unfortunately for all of us, there were too many doubts because of the way we started. Now he knows where he's standing, knows he's started later and knows he cannot play 90 minutes right now.
"He knows the importance of maybe the last half-hour for us. Hopefully then we'll see the Jozy of the last five games [of last season]. That's great for us. He knows his role in the team for the next month."
Altidore scored just two goals in all competitions last season.