United were swept aside by Barcelona at Wembley on Saturday as their quest for a double ended in disappointment.
And now Casillas, part of the Madrid side that lost to bitter rivals Barca in the semi-finals, has said: 'I believe 100 per cent, if Madrid had been in that final, we would also have overcome United.'
Helpless: Pedro Rodriguez (left) beats Iker Casillas in the Champions League semi-final
Casillas, who is in the Spain squad for their friendly with the USA this weekend, impressed in both legs of the Champions League semi-final but couldn't prevent his side losing 3-1on aggregate.
He added: 'I think in the semi-final between Madrid and Barcelona, that was the champions of Europe.
Party time: Barcelona lift the Champions League trophy after beating United
'The two best teams in Europe faced each other at that time.'
Madrid ended the season with just one trophy, the Spanish Cup, as they finished second to Barcelona in La Liga.
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