Manchester City's owners have built a team capable of winning the Champions League but will find it difficult to maintain long-term success, according to Real Madrid boss Jose Mourinho.
In an interview in Thursday's AS, Mourinho said the hundreds of millions of pounds invested in City in recent years had made them a force to be reckoned with on the European stage and a danger to Madrid in their forthcoming Champions League clashes.
"Manchester City are powerful because they have players at the highest world level," he said. "City are a team built to win the Champions League. The objective of the investment, made year after year, is to lift the European Cup. It will be tough. Tough for Real Madrid ... and tough for them because Madrid are Madrid."
Last Friday's draw saw Premier League title holders City and La Liga champions Madrid thrown together in a so-called Group of Death alongside last season's Bundesliga victors Borussia Dortmund and Eredivisie winners Ajax.
Mourinho said each team within the group could cause the others problems, adding: "Dortmund are two-time champions of Germany, a top team full of internationals, many from Germany and the best players from Poland.
"They are picking up experience in the Champions League, they have an impressive stadium and fans who support them till the end. With Ajax you never know, they could give you trouble. There is no margin for error."
Mourinho said he was confident that Madrid would progress but concerned that such a tough group could harm his side's prospects further into the competition.
"The two teams who come through our group, we will not reach the knock-out phase in the same conditions as the other 14," he said. "We will need to be at our best from the first minute and in every game through the group phase with the maximum of intensity, concentration, commitment and pressure.
"We will arrive at the quarter-finals with effort in our legs and our heads. The others will arrive fresher, and without yellow cards or suspensions, having rotated players to control the numbers of minutes played. We will arrive with physical and mental fatigue."
The Portuguese coach would not comment on the reasons behind Cristiano Ronaldo's recent "sadness" comments, but did say he was not worried that cash-rich clubs such as City or Paris St Germain would lure Madrid's best players away.
"Madrid, Barca, Bayern ... these clubs have unique historic capital," he said. "The trophies, the European Cups, the history, the fans ... things you cannot buy with money.
"The best players will want to be at these clubs, the three I have mentioned and some others who have trophy cabinets full for almost a century. That is a determining factor for the players."
The former Chelsea manager said he welcomed UEFA's forthcoming Financial Fair Play regulations, which would work in favour of Madrid and other big, traditional clubs.
"There will be difficulties for clubs which are not well structured, although they have wallets full of money," he said. "Madrid's structures are well prepared for this, and we can enter successfully into the new era.
"We have the potential and history to keep our best players, Cristiano Ronaldo, Iker Casillas, Karim Benzema, Gonzalo Higuain. Everyone in our squad, Barca, too.
"But clubs which live just from the investments from their owners will not have it so easy, because they do not have the structures of the historic clubs. In that way, Financial Fair Play will be good for football."