The Black Cats go into Sunday's Wembley showpiece as the underdogs, and their manager believes telling players they won't be featuring will be one of his toughest moments.
The Uruguayan is preparing his charges to contest the final of the first domestic trophy of the English season on Sunday, with Sunderland playing the role of underdog against Manchester City at Wembley.
Long-term injury absentee Keiren Westwood and the cup-tied Liam Bridcutt are the only certain absentees, meaning Poyet will have some tough selection decisions to make ahead of the game and he believes naming the squad ranks among the most difficult calls of his career.
"Leaving players out, that's the worst," Poyet told the Shields Gazette. "I read a great interview with [Real Madrid head coach] Carlo Ancelotti the other day talking about pressure - pressure of the fans, games, club and press. But the worst for him was the players. To tell an important player that they have not made the bench.
"It's tough to tell a player he's not playing, but to tell him he's not made the bench, is hard. It doesn't matter how honest you are or how clear the decision is, at the end of the day, the player is not in the matchday squad. That's the worst part for me."
Poyet is hopeful that, if required, Sunderland's substitutes can make the difference against City, and will draw on his own experience of coming off the bench to net the winner in Chelsea's 1998 UEFA Super Cup final victory over Real Madrid.
"It's happened to me [being left out]," he added. "I scored plenty of goals in my career, but for some reason, I couldn't score in cup finals. I played two in Spain, one in Paris with Zaragoza against Arsenal, and one with Uruguay.
"Then I came here and played a Charity Shield, but I couldn't score. I was scoring fine in semifinals, but you start thinking what is wrong with you? Then Mr [Gianluca] Vialli left me on the bench in the Super Cup. I was fuming. Then I went on in the 70th minute and scored the winning goal. What's better?"