Chris Cuomo isn’t a fan of Presidential debates, dismissing them as pageantry — but he says that’s not the case with the face-off next week between Joe Biden and Donald Trump.

Cuomo was on “TMZ Live” Friday … and his take is the debate will be a major test for Biden, not on policy issues but on cognition.

The NewsNation anchor breaks it down like this: If Joe steps onto the debate stage and performs well, then Trump’s gonna regret all those digs, like comparing him to cartoon characters and mocking his cognitive abilities.

But, if Biden looks like “poo poo” — Cuomo’s words, not ours — then it could change the trajectory of the upcoming Democratic Convention.

CC says he knows JB’s inclinations well — and believes if he gets roughed up in the debate, he’s going to have a “man in the mirror” moment — asking himself if he should throw in the towel and step aside … if it becomes clear he can’t beat Trump.