The Swede managed England for five years and led the national side to the quarter-finals of both the 2002 and 2006 World Cups.
Rooney went into the 2010 World Cup on fine form following one of his best seasons with club side Manchester United.
And Eriksson is unable to explain why the 25-year-old Red Devils forward failed to make an impact in South Africa, but still believes he is one of the best footballers in the world.
“I can’t explain [why Rooney did not have a good World Cup campaign]. To explain that you would need to have lived together with the team and seen the training and look at the ambient in the camp and things like that,” he told Yahoo!
“Rooney is one of the best footballers in the world, he has been for years now. He is extremely important for England and Manchester United. Sometimes we forget he is still young and has many years to play. He is a top player.
“The media builds up the team before the big tournaments, so before you have kicked a ball in a World Cup you have almost won it according to the media. This puts the players under big pressure, too much sometimes.
“You cannot live a life one month before the World Cup without reading a paper or without looking at TVs, so everyone is aware of that."
After his tenure as England manager, Eriksson became coach of Manchester City but was sacked after just one season in charge.
Eriksson feels he would have had more success had he taken charge of City under the current owners, but believes Roberto Mancini’s side have the potential to win the league in the near future.
“I came to Manchester City two or three years too early. I should have come with the other owners, that would have been great.
“If they [City] continue spending and buying like they have been, sooner or later they will win, and go on to win the Premier League and also a trophy in Europe. Maybe this year.
“Money is not enough if you are thinking about short term. I don’t think you can buy a team and in one or two years make it the biggest team in the world. You need more time.
“Money is necessary. You will not win the Premier League or Champions League today without money. It is impossible unfortunately."
Visit The Dugout for new interviews every week with England’s top football managers.
By Vaishali Bhardwaj
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