The £80million transfer fee for Cristiano Ronaldo has been described as "excessive" by UEFA president Michel Platini.
Real Madrid's offer for the Portuguese winger, which has been accepted by Manchester United, follows soon after the Spanish club's £56million swoop for Kaka.
Platini said in a statement: "These excessive transfers are happening almost every day.
"These transfers represent a serious challenge to the idea of fair play and the concept of financial balance in our competitions.
"UEFA are working hard with clubs to establish a new set of rules as soon as is possible to clean up the system and give it a more solid and more transparent base.
"That is our top priority today."
Earlier, sports minister Gerry Sutcliffe had called the £80million fee beyond the comprehension of the ordinary fan.
Sutcliffe, a Salford-born Manchester United fan, said the money offered by Real highlighted the growing gap between a few rich clubs and the rest.
The minister said: "These are astronomical figure and from the wider perspective this transfer, added to the one of Kaka [for £56million], continues to give us cause for concern.
"Competitive balance is not just a UK issue now, it's a European issue especially since Florentino Perez is now bringing the galacticos back to Real Madrid.g
"These figures are simply beyond the understanding of most ordinary fans.
"I am worried that a small group of rich clubs are getting richer and that does affect the balance and the opportunities for the wider game.
"It is what motivated us to write to the Premier League, FA and Football League to express our concerns about transparency and competitive balance."
Sutcliffe admitted that with Ronaldo wanting the transfer, £80million was too good a fee for United to turn down.
He added: "As a United supporter I am disappointed to see him go because he has been a wonderful player for us but I accept it's good business for the club to sign him for £12million and sell him for £80million."