With Rooney banned for the first two games of the group stage against France and Sweden, Keane believes the forward's ability to keep himself occupied will be tested to the maximum.
"Is it going to be difficult for him to focus? Definitely," Keane, who quit Mick McCarthy's Republic of Ireland squad at the 2002 World Cup, said in the Daily Star.
"English and Irish players are the same. I don't think we are good at hanging around hotels and training camps. I've experienced that myself as a player, at club level as well when you go away in pre-season for a couple of weeks.
"The big problem Wayne will have is the boredom, mentally trying to build up for a game. Wayne wouldn't be a great one for sitting around.
"As you get older, you might be married and have kids. You might appreciate the peace and quiet. But Wayne is still young, he's pretty active mentally.
"Roy Hodgson will have to manage that, get the balance of what he does on the training pitch right. He has to keep sharp, but without overdoing it or getting irritated."
England face Norway and Belgium in friendly warm-up games before meeting France in their Euro 2012 opener on June 9.
"If he's not playing in the first couple of games, I'll not expect him to play in the friendlies," Keane said. "So Wayne could go into his first game having not kicked a ball for four or five weeks.
"There are pluses and minuses. Sometimes players come back fresh. He'll be fresh and he'll give England something a bit different. Unless England win their first two matches, I imagine he'll be straight into the team.
"But it is not as if Wayne can feel his way into the tournament. It's 'you have to produce today'. As good a player as he is, that is difficult."
Keane does not envisage England going far in the tournament, and added: "You would expect them to get out of the group. I just don't expect them to win it. I would have been saying that if Capello was still there.
"There will always be pressure on the players from the manager to win the competition. England have good players, but I expect them to come up short again, like they have in the past.
"I just have this feeling for Germany or Spain."