Rooney scored 34 goals for the Red Devils in the 2009-10 season to fire the club to the Premier League title and also netted nine goals during England's World Cup qualifying campaign.
However, his recent form for club and country has dipped over the past year, and Carragher feels that the 28-year-old may already have produced the best football of his career.
Carragher wrote in the Daily Mail: "When you think of Wayne Rooney, what are your standout memories? I have three. The first is of him as a fresh-faced and fearless 18-year-old, lighting up Euro 2004; second is his magnificent season in 2009-10 when he fired 34 goals for Manchester United and was named PFA Player of the Year.
"Third comes the 2010 World Cup qualifying campaign when he scored nine times under Fabio Capello. Others will have their own highlights but it is doubtful anyone will place Wednesday's game against Norway at the top of their list.
"Though he marked his first match as captain with an emphatically dispatched penalty, nobody was in a hurry to shout about his display. If anything, it raised a question - have we seen the best of him?"
Rooney scored his 41st goal for the Three Lions in his first match as captain in his side's 1-0 win over Norway on Wednesday.