As a Man United fan, haven watched Cristiano Ronaldo played some matches in Man United, has he made a mistake of coming to the club or the club made a mistake of buying him?

Both made mistakes.
For Ronaldo, it's obvious he's never going to win the highest goalscorer award in EPL till he leaves. Also, his chances of winning even a Carabao cup is slim.
Ofcourse the situation would've been different if he had joined man city instead. The EPL, FA Cup and Carabao cup would've been guaranteed within 2 years. His chances of winning the top scorer would've been high too compared to now that he's in United. Also, man city would win the UCL within the next 3 years, it's fact. If he had joined them, and they won it, he would've been a legend automatically as they would say he led them to their first ever UCL trophy.

Man utd should've added a little money to the money they spent on Ronaldo on a good CM.
They didn't need Ronaldo. Cavani is there. Rashford can play as a striker too.
The moment they signed Sancho, they should've never signed Ronaldo.
Ronaldo has completely destroyed the work ethic of the once great team. They propably didn't see why he was getting benched at juve.

Most of u dont do research...Ronaldo haters trying to blame uniteds top scorer this season...below is man utds points after week 8 and 9

Big mistake.

united do mistake sign am jus bcox dm wan out do city...na wen season end them go realize n understand the mistake

MangekyoAlt:
Both made mistakes.
For Ronaldo, it's obvious he's never going to win the highest goalscorer award in EPL till he leaves. Also, his chances of winning even a Carabao cup is slim.
Ofcourse the situation would've been different if he had joined man city instead. The EPL, FA Cup and Carabao cup would've been guaranteed within 2 years. His chances of winning the top scorer would've been high too compared to now that he's in United. Also, man city would win the UCL within the next 3 years, it's fact. If he had joined them, and they won it, he would've been a legend automatically as they would say he led them to their first ever UCL trophy.

Man utd should've added a little money to the money they spent on Ronaldo on a good CM.
They didn't need Ronaldo. Cavani is there. Rashford can play as a striker too.
The moment they signed Sancho, they should've never signed Ronaldo.
Ronaldo has completely destroyed the work ethic of the once great team. They propably didn't see why he was getting benched at juve.

Oga trash talker... How can a bench player win SerieA golden boot?

I will tell you the truth. Ronaldo is a good 'finisher' but the team right now needs more than that from a player of his class. They need him to run around, get more involved, call more shots. If standing in the front goal is what a player does every time, then accolades for the goal records of that player should only go to team mates who are usually more involved in the buildups to that goal.
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However players like Timo Werner have, countless times showed that scoring clear goals and making perfect finishings can be a daunting task...ad with a coach like they currently have, it wouldn't be nice to exactly blame any player right now.
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That coach however is doesnt deserve all the guilts and blames too. He has done what other successors of Ferguson could not do even while being denied of the key central midfielder he is consistently asking the board for and he did all these without our super player Ronaldo.
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When we compare what other players are doing in their respective clubs however, you can say players like lewandoswki, Halland and ronaldo are players you need when you already have a smart team with a good team work. Or perhaps when u have a bad defence and you need to put in a lot of goals to always conceal your errors.
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But when your needs are from the center, when you want someone to do more runnings, when you want a team with that 'strong outlook' you need a coach like tuchel or pep and a player like Messi, Mbappe, Suarez or even Ramos.
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Ronaldo is certainly a great player, doing his best to do what he does best (banging in goals)
But honestly, he might leave Manchester in more shambles than juventus.