The five-time Ballon d'Or winner returned to action in Europe on Wednesday, after a spell on the sidelines with a muscular injury picked up while on international duty with Portugal.
The 34-year-old showed no signs of rustiness though, as he grabbed Juve's goal in a 1- draw at the Johan Cruyff Arena which has left the tie delicately poised.
Allegri's main goal this season is to conquer the Champions League, with the Serie A title virtually a foregone conclusion heading into the final weeks of the campaign.
Ahead of that fixture, Allegri revealed that Ronaldo will be granted an extra day off to recover from his exploits in midweek.
“Risking tomorrow makes no sense," the Italian head coach began.
"And like him, this also goes for our other players who have been playing a lot even during the breaks for their National teams.
"However, I will line up a tough and fair formation for the challenge that awaits us".
Allegri also suggested that he could give a few younger members of his squad an opportunity to shine against SPAL, with the likes of Leonardo Bonucci and Mario Mandzukic also likely to be rested.
He also confirmed that 19-year-old Moise Kean will return to the starting line up, after his impressive recent goalscoring run.
“I have to evaluate today's training session, but many players will rest," he added. "There are players who need to rest. And maybe tomorrow will be an opportunity for some young players to play. Either one of Nicolussi Caviglia and Coccolo could play tomorrow. Kean starts."
“Mario has a way of playing that sees him give his all. Those who played the World Cup final have a much greater load.
“Leonardo is fine but he could rest tomorrow”.
If they secure the Serie A crown on Saturday, Allegri can then focus all of his attention on the Champions League, with a semi-final tie against either Tottenham or Manchester City to look forward to if they can get past Ajax.