And with United possibly having up to 14 games left to play this season, manager Ferguson insists that Rooney is capable of surpassing even Ronaldo's mark.
Manchester Uniteds defeat calls Premier Leagues claims to be the best into questionFerguson said: 'It's a challenge [for Rooney to get 42 goals]. I was just happy for him to reach 30, to be honest with you.
'But he keeps on improving and he was sensational again tonight.
'He is still carrying an injury, nothing serious, but with a game on Sunday (against Fulham) we wanted him off early.
"His performance was a continuation of his form over the last two or three months, just sensational, unbelievable. I'm very pleased with him.
"What's improved is his movement in the penalty box. He's also practiced a lot more than he has ever done.
'After training, he puts extra work in and that's what we're seeing now - he's reaping the rewards of that.'
Ferguson, who has shelved plans for midfielder Owen Hargreaves to end his 18-month injury absence in the reserves on Thursday night, claims that United's victory should not be under-estimated.
He said: 'We beat Milan 4-0 and not many teams have done that. I don't know if anyone has done that.
'The deciding factor was Rooney's goal just after half time. That finished the tie.
'We were able to relax, play good football and keep our concentration after that.
"Milan had to force it and that made it difficult for them.' David Beckham, making his first appearance against United at Old Trafford, was afforded a rapturous welcome when he entered the fray as a second-half substitute.
Beckham said: 'I have to say thank-you to all of the fans because they were incredible.
'It was nice to be back. It was obviously a disappointing night, but nice to be back.'