Kepa was at fault as Manchester City stunned Arsenal in the Carabao Cup final a fortnight ago.
However rather than recall first-choice David Raya for the Cup tie, Stack believes Kepa will be played.
He told The Sun: “I think he’ll stick with him. I think he’ll restore some confidence in him.
“I think he’ll probably have a little chat with him this week and reassure him that he is a great goalkeeper, or can be a great goalkeeper, to put it behind him and back him.
“Because I think when you get that backing from a manager after a big mistake, I think that speaks volumes about a manager. But it also gives you a massive lift as well.
“I thought it was definitely the right thing to do – Kepa was excellent in the run-up to the final. I think he deserved to play in the final.”