The club's chairman told The Express: "I will lose him, I don't think there is any question about that. He is a top-class manager and he will get one of the top clubs in Europe.
"The big clubs in Europe, when they want a manager, Roberto is obviously the man. He is stone-cold brilliant as a manager.
"If we win the Cup and stay in the Premier League, I will promise him a huge pay rise."
Wigan are currently in the Premier League's relegation zone.