Brown won Europe's biggest prize alongside Ronaldo in 2008.
He reckons Ron is ready to star again when he returns to Spain for the last-16, first leg tie against Atletico on Wednesday night.
For 888Sport, Brown told The Sun: “This is him. He is the Champions League, isn't he?
"These Champions League nights, they are a bit different to playing domestically.
“They can be special and he is the one that steps up into another league.
“People always say to me, 'What was it like? He never defended?' I say it didn't matter. He took two or three players away. I didn't have to do anything.
“He still gets in positions to score. He's done that the last few games and that's all you can hope for from a player.
“If he doesn't get into these positions, it would be different, but he does. If Manchester United are more consistent, then he will get more opportunities to score."