José Mourinho has admitted it is impossible for Chelsea to compete financially with Manchester City since the introduction of the financial fair play rules.

Chelsea were the biggest English spenders during the January transfer window but their outlay of £45m was more than covered by the sales of Juan Mata and Kevin de Bruyne for a combined £55m. They had aspired to sign the Porto centre-half Eliaquim Mangala but were unwilling to risk their compliance with Uefa's regulations by sanctioning an outlay of around £37m. City are expected to pursue that deal in the summer.

Yet while there is scepticism at Chelsea that their rivals, principal among them City, simply exploit loopholes in Uefa's regulations – Mourinho described it as "dodgy" financial fair play on Friday – they intend to follow the rules even if that means they cannot compete on such fees.

"If City want to make it impossible, yes it's impossible because we are not competing outside what is important for us: the fair financial fair play," Mourinho said. "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. Financially, no [we can't compete]."

He referred to Roman Abramrovich's arrival at Stamford Bridge a decade ago. "Back then it was a free world. 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."

Asked about Mangala, Mourinho added: "We can't. We signed [Kurt] Zouma [for £12.5m], who is even younger and a comparable figure."

Asked about the popularity enjoyed by City – born of their attractive, attacking style – among neutral supporters, compared with that of his Chelsea team during his glittering first spell in English football, 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.

"I don't envy the fact that they have this kind of protection, or whichever word. It's the way it is. No problem. Teams with success, people tend not to like, no? But times change. Many things people considered wrong 50 years ago are something very normal now."Maybe 10 years ago a huge investment in the club was something people hated, but in this moment it's something people accept in a different way. If Uefa goes with FFP until the last consequence, 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."