Rooney scored the winner against Ukraine in Kiev, but struggled to make an impact in the Three Lions' quarter final match against Italy, looking off the pace.
The 26-year-old striker missed the first two games of the tournament through suspension as a result of his sending off in the final qualifying game against Montenegro.
And his club manager believes the significant gap between his final competitive game of the season for United and his first game at the European Championships had a detrimental impact on his performance.
"I always thought it was difficult," Ferguson told Sky Sports. "We know him better than anybody and he needs a lot of football.
"Wayne's a stocky lad. If he misses a couple of games, it takes him three or four to come back.
"He didn't look as sharp as normal [against Italy]. It is very hard to play two big games in four days."
|UNITED MISS OUT ON TOP FOUR|
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After coming to prominence on the international scene as an 18-year-old with a string of sensational displays at Euro 2004, the former Everton striker has failed to make a significant impact at a major tournament since.
However, his impressive club form and 29 goals for his country to date has seen him identified as one of the national team's biggest talents, and the Old Trafford boss believes that United No.10 must learn to deal with the intense pressure that comes with his ability.
"It's a fact of life," the 70 year-old added.
"I read an article that Argentina have never taken to Messi. Then he goes and scores a hat-trick against Brazil with that incredible third goal."
"People were saying Spain weren't the force they were, then Xavi produces the kind of performance he did. It was brilliant.
"Great players have to deal with these things."