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Rijkaard was critical of the English team's style of play
Barcelona paid the price for a lack of cutting edge as United repelled wave after wave of attacks.
Rijkaard conceded United had defended well but was also critical of what he felt was their negative tactics.
"The level of English teams is high," he said. "It is very difficult to beat them because they are very strong.
"They are very organised and all get behind the ball. It is very tough to beat an English team.
"The type of football they play is only in the Premier League. They defend as though their lives depend on it. And they are very successful.
"But I do feel English teams have a lot more to give. I just feel it is a great pity it is not the most beautiful kind of football to watch."
Spanish websites said Barcelona's defeat signalled the "end of an era" for the Catalan club.
They have failed to keep pace with fierce rivals Real Madrid in La Liga and Dutchman Rijkaard looks certain to be dismissed at the end of the season.
"Barcelona are a massive club and there are people to take the decisions at the end of the season if decisions need to be taken," he added.