Roman Abramovich's fear of the impending UEFA Financial Fair Play rules and potential exclusion from the Champions League is behind the Chelsea owner's refusal to pay the full asking price for David Luiz.
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UEFA president Michel Platini's bid to curb the spending excesses of the top clubs has caused Abramovich to be far more conservative with his spending, and the same sobering effect may also be felt at Manchester City.
Even if Abramovich finally sanctions the narrowing difference, after three failed bids, between the £18 million offered and the £25 million demanded by Benfica for their outstanding young Brazilian defender, it can no longer mask the real reason behind the end of his big-spending ways.
The new rules come into force for the 2012-13 season.
One of the men involved in the transfer dealings of Chelsea and Manchester City spoke to ESPNsoccernet about the concerns affecting the Premier League's big-spending clubs.
The source said: "The problem at Chelsea is that it is vitally important for the team that they acquire a central defender; one of the highest quality, young and who can come straight in and make a difference.
"David Luiz is that man, he is by far their first choice, but after three failed bids there is still a gap - one that is getting ever closer, but still a gap. There is a deep reluctance on the part of Chelsea to pay the full amount demanded by Benfica.
"The reason is simple ... UEFA's new Financial Fair Play regulations come into force in a year or so, but clubs buying now and paying later will be hit hard if they find they are spending more than they are earning when those rules come in.
"This might turn out to be the window of the last of the really big buys. Certainly there might be one or two, but nowhere near as many as in the past."
Chelsea are also looking at Atletico Madrid's Diego Godin and Simon Kjaer at Wolfsburg. English alternatives such as Gary Cahill are being considered, but Bolton are demanding £20 million for a player on the fringe of the England squad, and Chelsea believe that is excessive.
Another alternative is to take one of Manchester City's surplus players, such as centre back Joleon Lescott.