The Aston Villa assistant manager was pessimistic about Roy Hodgson's side's chances before the start of the tournament. However, he has revealed that he was taken aback by the Three Lions' exit from the group stage without winning a single game.
Keane told The People: "I wasn't showing football knowledge. I was asked whether they would struggle or do really well. I said they'd struggle. But I didn't think they would struggle that much.
"If you look at the squad, they should have done enough to get out of the group. But a lot of them still lack vital experience – whether it's Champions League experience or big-game experience.
"People are ranting and raving about the younger players, but they still have a lot to do. A lot of them are yet to win a trophy, yet people still expect them to go to the World Cup and get to the quarters or semi-finals."
Keane joined Villa this summer as number two to Paul Lambert in addition to his duties as assistant boss of the Republic of Ireland.