Hiddink, after guiding Chelsea to success in the FA Cup final, has returned to his job as coach of the Russian national team, but was forthcoming in his assessment of where it went wrong for United in Rome.
When United and Barcelona were paired in the final of the continental competition it was the match most neutrals wanted, with a belief that a classic was on the cards, though it turned out to be a decidedly one-sided affair.
Goals from Lionel Messi and Samuel Eto'o sealed a 2-0 victory for the Catalans on a night when United were outplayed by their Spanish opponents.
But Hiddink believes United may have fared better had they been cute to a couple of tactical adjustments by Guardiola.
'I had no joy watching the Champions League final,' said Hiddink in the Express newspaper.
'It was boring. There was only one team on the pitch. And it was Barca.
'There was no real fight and it was proof that it's very important to analyse the opponent.
'Barcelona played their own football, but they also knew in advance all the weaknesses of Manchester United.
'Lionel Messi wasn't playing as usual on the right in the attack but moved more to the centre. And Samuel Eto'o moved to the right.
'Those tactical changes showed Barcelona thought in advance how to cause United maximum damage.'