The 28 year-old has played alongside both players for his club and country, giving him a rare insight into their respective qualities.
He played with Ronaldo for two seasons at Old Trafford between 2007-09, but his allegiance is, not surprisingly, with his countryman Messi.
"I think it is only right if Cristiano Ronaldo does believe he is the best in the world," said Tevez.
"Any guy who gets 37-40 goals a season has a right to believe that, but if you push me I am always going to go on the side of Messi.”
Messi and Ronaldo are perennial challengers for the Ballon D’Or, their goalscoring feats unparalleled throughout Europe.
Regardless of where Tevez believes the balance of power currently lies, he knows Ronaldo is the player most likely to end City’s distant hopes of a European revival.
"Cristiano is one of the best players in the world and he will play in this game the way he always has done. He does not seem to feel pressure. We will have to keep a special eye on him," said Tevez.
"I think that you have got to try and make sure he doesn’t get in behind you. Once he gets a chance to run at you he is very dangerous and he strikes the ball well, too, so you have to try and stop him further up the field."
Only a win will prolong City’s interest in the Champions League, and even then they’ll need an unlikely sequence of results elsewhere to work in their favour to transform a grim situation.
Manager Roberto Mancini admits he doesn’t expect the miracle to happen, but Tevez says hope remains.
"The players are all convinced it is still possible. As long as it is mathematically possible, why not?" he said.
"It is true that it is a really tough group, possibly the toughest in this year's Champions League, but let's not consider that as an excuse for why we have not got the necessary points."
The Italian appears to have been granted a tab in the last chance saloon, but there are growing signs his manager has now lost patience.
"Mario, outside the pitch, is a fantastic guy but sometimes he doesn't understand his job, and how his job is important for his life," said Mancini.
"I hope for him that he can understand this quickly. Now he is 22, but life can go quickly and I hope he can improve everything because as a player he could be like Cristiano and Messi.
"He needs to understand that to be like this you should work hard and your mind should always be on your job, not on the other things that are not important. I am very sorry for him if he does not understand this because he has everything to be one of the best players in the world."
Balotelli has missed City’s recent fixtures, which took them back to the top of the Premier League, after being dropped against Spurs, and then suffering a back injury while on international duty with Italy.
He is unlikely to feature against the Spanish champions.
By Chris Bascombe Telegraph.co.uk