The Italy international was one of former manager Paolo Di Canio's biggest signings of the summer at £6.5m but was stuck on the bench last Sunday.
"He is frustrated, he is not happy," Poyet revealed on Thursday.
"It's difficult for him to take being out of the team, but I'm sure that when the results go against you, the problem is even bigger and we won the game. I'm expecting Giacci to be ready. He will play, a lot. I can't give him everything he wants because he wants to play every game for 90 minutes but he will play a big part for us."
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