The draw meant Juventus, who remain top of the Serie A table, dropped their first points of the season.
Since 2003, Ronaldo has tallied 311 goals for Real Madrid, 84 goals for Manchester United, and five goals for Juventus.
"But we have to take the positives from the game and I think the way we played in the second half especially, we were fantastic at times".
At one stage, Ronaldo looked to be in danger of missing the game entirely after he was shown a red card in Juve's Champions League opener against Valencia for pulling Jeison Murillo's hair, but in the end he was only given a one-match ban.
With Genoa struggling to contain the lively Cancelo down the right Juve were firmly in control, their only regret at the break being they weren't further in front.
Energised, the 23-year-old should have levelled seconds later, outjumping Leonardo Bonucci but his header went wide.
"It will be a great Champions League night, United are strong, and like us they will also try to win".
The visitors were eventually rewarded in the 67th minute when Daniel Bessa caught the Juve defence napping and nodded home from close range.
Allegri responded by introducing Paulo Dybala for Blaise Matudi as a frantic finale beckoned with Genoa holding on for a surprising point. Every match has to be won on the pitch in 90 minutes.