Aguero is set to make his Manchester City debut on Monday night against Premier League new boys Swansea and Messi is convinced the former Atletico Madrid striker will be a success.
"I have no doubt that he will be successful at City," Messi was quoted in the Sun as saying.
"He will give them a real cutting edge. He's unique - he has immense power, strength and an incredible work ethic. He will certainly stand out in terms of what he will bring to City.
"Defenders will find him so difficult to play against.
"There is no doubt in my mind that City have signed a very exceptional player."
Messi, who is recognised by FIFA as the best player on the planet, thinks the club have shown a serious sign of intent to win trophies when they chose to splash out £35million on Aguero.
"Aguero is flexible and can play in a number of positions. Adapting to the pace of the Premier League won't be a problem," Messi said.
"Carlos Tevez has been a huge success in England and Aguero will be no different.
"I think it shows the serious intent of Manchester City when they are signing a player of his quality.
"Personally I would have loved to have seen him stay in Spain and preferably move to Barcelona.
"But he was excited by the challenge and ambition of City. Money isn't a motivating factor for him. He loves a challenge.
"More importantly, he wants to win trophies and obviously feels the move offers him that opportunity in England."
The 23-year-old Aguero is still some way short of full fitness and City manager Roberto Mancini is expected to include Aguero on the bench for Monday's season opener at home to Swansea.
Manchester City vs Swansea City Team News
Argentina striker Carlos Tevez only returned to training this week and, with his future still uncertain, manager Roberto Mancini does not feel it is worth pushing the 27-year-old into the fray against Swansea.
Tevez's international colleague Aguero may, therefore, be involved for the first time since his club-record £38million move from Atletico Madrid, although Mancini reckons he could contribute only 45 minutes at best.
Captain Garry Monk is a major doubt for Swansea.
The defender, who signed a new three-year contract earlier this week, is struggling with a foot injury and may have to wait for the home clash with Wigan to make his first appearance of the campaign.
Goalkeeper Michel Vorm comes straight into the squad after completing his move from FC Utrecht and will battle fellow new signing Jose Moreira for the starting berth. Danny Graham, Leroy Lita, Wayne Routledge and Steven Caulker are also in line to make their debuts at Etihad Stadium.
Manchester City (from): Hart, Pantilimon, Taylor, Richards, Zabaleta, Savic, Kompany, Lescott, Clichy, Kolarov, Boyata, Johnson, Barry, De Jong, Milner, Silva, Toure, Weiss, Wright-Phillips, Balotelli, Dzeko, Aguero.
Swansea (from): Vorm, Williams, Taylor, Caulker, Tate, Bodde, Britton, Orlandi, Beattie, Graham, Sinclair, Dyer, Cornell, Dobbie, Routledge, Monk, Cotterill, Lita, Moore, MacDonald, Moreira, Rangel, Harley, Agustien, Butler.