Manchester City have not guaranteed Champions League success by appointing Pep Guardiola, according to his former player Sylvinho.
Sylvinho, now Inter's assistant boss, won Europe's elite club competition under Guardiola at Barcelona in 2009 before going on to finish his career at City.
Sylvinho hailed the quality of the Bayern Munich head coach, who will replace Manuel Pellegrini at the Etihad Stadium from the 2016-17 season after agreeing a three-year deal.
But while he believes City have ensured they will be playing great football, the ex-Arsenal defender still thinks Guardiola has a tough ask to win the Champions League.
"The Champions League is not easy at all," Sylvinho told Omnisport.
"Manchester City are working in the correct way, they have got some players, a new coach. They give managers time - Pellegrini got three years, Mancini started his work many years ago.
"It is very important to leave two or three seasons for each coach and now Guardiola has got time to work on the Champions League.
"I am absolutely sure Manchester City will play great football, but to win the Champions League in three years is not easy, it is difficult to say that. But they will try to play great football all over the world.
"Of course it is part of the plan for Man City to bring in Guardiola to build a new team to go to the final of the Champions League and to try to be champions, but it is not easy and he knows it."
Sylvinho also thinks English football will introduce new challenges for Guardiola as he continues his trophy-laden coaching career.
The Brazilian added: "I remember the Premier League. It is unbelievable, really intense, one of the best countries to show how he works.
"It is a good challenge for Pep, the Premier League is not easy at all. In winter there are difficult pitches, the stadiums are difficult with unbelievable atmospheres - one of the hardest leagues in the world.
"I had a great opportunity to work with him in Barcelona. Of course he is one of the best coaches in the world, no doubt about that, but we have got two, three, four more coaches that are at a high level. What I can say about him is his teams play unbelievable football."