Chelsea boss Jose Mourinho believes it will be "impossible" for clubs to compete with Manchester City if Financial Fair Play is not enforced.
City's vast spending in an era of Financial Fair Play has come in for repeated veiled criticism from Mourinho, who is keen to see how the economic regulations are explained and enforced by European football's governing body UEFA.
"If they (football's authorities) want to make it impossible (to compete with City), it's impossible," Mourinho said.
"(Chelsea) are not competing outside what is important for us, the 'fair' Financial Fair Play.
"We are working, thinking and believing that Financial Fair Play is going to be in practice.
"So there are things that are impossible for us (to do)."
Mourinho, whose Chelsea team face City in a crucial top-of-the-table battle on Monday night, speaks from experience after recruiting many players for large sums during his first spell as Chelsea boss at the start of Roman Abramovich's Russian revolution.
When Mourinho first worked in England he admits "it was a free world".
He added: "There was no Financial Fair Play. If your club was a rich one, your owner a rich one, there were no rules. It was an open situation."
It meant Chelsea were unpopular. City, however, are playing a brand of football so scintillating and scoring so freely that they are attracting admirers.
Mourinho said: "In my time we were accused of buying the title, no? Because our owner was Mr Abramovich, just arrived in the country. Maybe now people see City in a different way.
"Times change. Maybe 10 years ago a huge investment in the club was something that people hated and in this moment it's something people accept in a different way.
"Probably, if UEFA goes with Financial Fair Play until the last consequence and they explain really to the people what Financial Fair Play means, maybe in that moment people will realise that some teams are different to other teams.
"But it's something I don't think about at this moment."
Mourinho has long described City, who were beaten 2-1 at Stamford Bridge in October, as favourites for the title and he has claimed Chelsea finishing second in the Premier League this season would be an achievement.
"If we finish second it's fantastic," he said.
"If we finish second doing the formation work, it's an acceleration of our process. If we finish second it's good."