Ronaldo was forced the pitch off with a thigh issue in Portugal’s 1-1 draw with Serbia Euro 2020 qualifying on Monday night.
Allegri says he won’t be gambled for the match on April 10 on the off chance that he accepts there is a danger of irritating the damage.
“He’s already started to move but he won’t return to training until he feels fit,” the Italian said.
“There is a risk he’ll miss the first leg against Ajax.
“We have to be careful because we’re in a tricky period of the season.
“It’s better he misses one match and comes back when he’s 100 per cent so there’s no risk of a repeat injury. It’s better to miss one match than two months.”
Juve are on course for there eighth Serie A title in succession and Ronaldo has been critical to their charge for both Local and European competitions with 24 goals in all competitions since his late spring move from Real Madrid.
In the wake of enduring the damage, the 32-year-old was insubordinate and asserted he had no worries about being out long haul.