The Portuguese forward, a five-times Champions League winner and the competition's all-time top scorer, has scored 21 goals since moving from Real Madrid and will be reacquainted with one of his favourite victims at the Wanda Metropolitano.
Ronaldo, 34, has scored 22 goals against Atletico, including a hat-trick in a Champions League semi-final first leg in 2017, a penalty in a 4-1 win in the 2014 final, as well as converting the final spot-kick in a shootout win in the 2016 final.
"We are not obliged to win just because we have Cristiano, we must also work hard all over the pitch and have our share of luck, which is also important," Allegri told a news conference.
"Having him is an advantage, but it's not all about Ronaldo. We have to remember we are facing a team who are very good in defence and very dangerous from set pieces and have done very well in Europe in recent years."
Allegri, whose side are top of Serie A and are unbeaten in the league, said midfielder Sami Khedira had stayed in Turin for medical reasons, with the club later releasing a statement saying he had an irregular heartbeat.
Atletico coach Diego Simeone said he would monitor influential midfielder Koke's fitness before deciding whether he would start against Juventus, adding that Diego Costa was not ready to play the whole game.
Spain international Koke was given the all-clear to play in Wednesday's game, after almost a month on the sidelines with a hamstring injury, along with Costa, who has only just returned from over two months out following foot surgery.
"We will have to see how he (Koke) feels tomorrow but he's enthusiastic about playing and full of hope," Simeone said.
"I feel very excited about being in the Champions League again, in such a great competition and against such a powerful team. After not making it (to the knockout stages) last year, we want to make it to the next round to grow as a team and a club."
(Reporting by Richard Martin; Editing by Christian Radnedge)
