Allegri said Ronaldo – the all-time leading goalscorer in the Champions League – would deliver against United.
“He will score [on Wednesday],” he said.
“He didn’t play the first match, he didn’t play the second, he played only one match. And he provided an assist.
“I mean, it’s not like he played many Champions League matches so far.”
Juventus hold a perfect record in Group H and will seal their place in the knockout stage if they avoid defeat against United.