I have my doubts. This sounds to me like it should be filed alongside those other, rather flimsy Brazilian stories that have become 'print the legend' fixtures online, Pele and Romario's 1,000 goals.
The primary source for the Ronaldinho story seems to have been an interview with Four Four Two writer Andy Mitten in January 2006. It remains the source cited on Ronaldinho's Wikipedia page, even though the link to the article, headlined 'The Master', is now broken. I'm assuming the article took the story from the horse's mouth, as it were, but, unless I can find the article, have no way of knowing.
The fact that no one seems to have named either of the sides involved in the match, where it took place and in what competition (a lot to ask, I know given Ronaldinho's age at the time he supposedly pulled off the feat) makes me suspicious. I'm also intrigued to see that Ronaldinho's Portuguese Wiki page doesn't include any mention of the 23-0 game.
I'd love to be wrong, of course. But I think I need to see more evidence. I am certainly going to keep looking and would really appreciate any steers in the right direction.