Keane last month questioned England fans for treating Grealish as if he is “the Messiah” of English football.
But after his excellent display against Ireland, Keane said: “We are always questioning about his end product, that has improved over the last six months. It was a cushy night for him. It was his second start, this guy is going onto great things, no doubt in my mind.”
Keane, working as a pundit for ITV, added: “Jack has said his experience coming into the England squad, working with top players, you cannot beat it. You talk about coaching, I think sometimes you learn more from working with better players and we can see that, even from a couple of appearances he has had for England.”
Fellow ITV pundit Ashley Cole also praised Grealish’s performance.
Cole said: “He controlled the wide areas, he controlled inside areas and he was very good on the ball. He decision making was better, he was linking up well with Dominic Calvert-Lewin and Bukayo Saka out wide. People always argue and say he needs to create more but he got an assist and was very good.”