However, he added Juve "do not win automatically" just because they have the Portuguese superstar.
Juventus take on Atletico Madrid on Wednesday at the Wanda Metropolitano in the first leg of arguably the most intriguing tie of the last 16.
Allegri said ahead of the clash the Italian champions will need all the team to contribute if they are to go all the way in the tournament this season, per Perform (h/t AS):
"It is not a question of obligation. The Champions League is a goal. You need to play well and be lucky. Having Ronaldo is definitely an advantage, but it is the team that has to play important games.
"Ronaldo is the best in the world, and you have more chances to win it with him, but you do not win automatically. The Champions League has always been a goal for Juventus, and it will be an important match [on Wednesday], as all the knockout stages played in the last few years have been."
Ronaldo's move to Juve last summer immediately gave their hopes of winning the tournament for the first time since 1996 a big boost.
The Old Lady have reached two of the last four Champions League finals but lost on both occasions.
In Ronaldo, they now have the tournament's all-time leading goalscorer.
He only scored once in the group stage, but his remarkable recent record in the knockout rounds is a good sign for Juventus:
Cristiano Ronaldo has only scored one goal in the Champions League this season but the knockout stage is where he comes alive. Ronaldo will be judged at Juventus for what they do in Europe. Read @_WrightJosh's preview on tonight's game in Madrid -- https://t.co/acqGL4zSmY https://t.co/vP3MFBPlOs
As is his record against Atleti, a team he so often tormented when he was at Real:
After topping Group H, Juventus could hardly have asked for a tougher last-16 draw than a tie with Atletico.
The Madrid outfit are seasoned Champions League campaigners and have also reached two finals recently, in 2014 and 2016.
However, Juve are favourites to advance to the last eight, and Ronaldo will be looking to get a crucial away goal on Wednesday when he returns to Madrid.