The manager said: 'In Ronaldo, I thought we had a player who could win the match. He was a constant threat and, with better support, we could have won.'
Ronaldo could have won them the game, had he not missed a penalty.
But he told Sky Sports: 'Today, I didn't score - no problem. Now I'm going to score in Manchester.'
He also refuted accusations from some quarters that he changed his penalty-taking technique, saying: 'I did not.'
Ferguson also felt let down by his side's midfield, saying: 'I am a bit disappointed in the transition between defence and attack.
'We are normally better at keeping possession of the ball, that causes more concern than any other part of the game.'
He also claimed his side surrendered possession too often.
'We will analyse (why we didn't score) in the next two to three days, but we lacked penetration,' he said.
'We were not quick enough out of central areas and when you give the ball away at this level, you have to go back and defend.'
He promised that United would go for broke next Tuesday at Old Trafford in search of a Champions League final place.
'Absolutely, no question about that,' he said. 'The game now starts at Old Trafford - it's the deciding game.'
Barcelona let United off the hook after failing to turn their domination into goals.
'It was a shame we didn't get the goal we deserved,' striker Samuel Eto'o said.
'It isn't enough to threaten, we have to score. But if we play like we did today when we go there next Tuesday, then we can go through.'
REUTERS, AGENCE FRANCE-PRESSE