Ronaldo has backed Jose Mourinho to turn things around at Manchester United, although he believes the Champions League will be staying at Real Madrid this year.
Mourinho is under pressure after United started the Premier League season with one win and two defeats, including a 3-0 loss at home to Tottenham on Monday.
He takes United to Burnley on Sunday with his future hanging in the balance, but Ronaldo believes a knee-jerk reaction would be wrong.
"I don't know what's happening in Manchester, but wait before criticising Mou -- he's special and he's won a lot," he told Italy's La Gazzetta dello Sport.
United have been drawn against Juventus, Valencia and Young Boys in the Champions League, with Paul Pogba and Cristiano Ronaldo facing their respective former clubs.
"[Juventus] are a really strong side," Ronaldo said. "They've reached the final twice recently and Ronaldo is going to strengthen them, but the Champions League is not easy. Signing Ronaldo doesn't automatically mean you win it.
"What you cannot deny is that it's a huge signing -- unthinkable -- but nobody can predict what will happen and how the balance will change. I wish him all the best. He will see what a beautiful country he's arrived in, and I love Italy. He's going to enjoy a great adventure.
"There is no doubt what he wanted. He was looking for a change of scenery and he has every right to do it. Real Madrid will always be very grateful to Ronaldo.
"At Real Madrid there will always be people who score goals. They are a team and not a single player no matter how much one appears more than another. Football is played collectively and everyone contributes."
Ronaldo played 68 times for Inter Milan, scoring 49 goals, and he is delighted to see them back in the Champions League this season, even if he is tipping Real for a fourth straight title.
"They are always in my heart, even if I've followed them little recently and not spoken any more with [former owner Massimo] Moratti," said the 41-year-old.
"They're back in the Champions League and that's a great result, and they are back among the best, which is where they belong.
"I'm very attached to Real, more so than Barcelona. Real were strong even before Ronaldo came and they will remain so after. They are still the favourites to win the Champions League. They've won four of the last five, although it's going to be a whole different challenge without Ronaldo."
Ronaldo has also backed fellow countryman Neymar following the Paris Saint-Germain star's underwhelming World Cup with Brazil and says the forward is still ahead of Kylian Mbappe.
"The World Cup was not a great month for Ney, but he has much more than Mbappe even though he is a good youngster, with a lot of pace," Ronaldo said.
"I read a lot but nobody from Real Madrid made interest clear [in Neymar]. All good players are interesting. Nine out of ten teams will want Neymar.
"PSG have a very good team, but to win the Champions League something more is needed. Teams are a collective expression."