Europe's top leagues have warned FIFA not to rush a decision on switching the 2022 World Cup in Qatar from summer to winter.
The scorching heat of the Middle East summer has led to a re-think about the timing of the tournament, with a move to November or December being mooted.
That has led to anger amongst the European clubs and Leagues - a switch to winter would mean the tournament being played in the middle of their domestic seasons.
The world governing body is due to decide on a switch at a meeting on October 3-4, but the Association of the European Professional Football Leagues (EPFL) - which includes the Premier League - has called for this to be postponed pending a full investigation into the effects of such a move.
FIFA president Sepp Blatter revealed on Monday that he will recommend a switch to the winter and UEFA president Michel Platini also wants a change.
But the EPFL said in a statement: "The feasibility of any change to the calendar involves every aspect of football organization across all countries, from the grass-roots to the major national representative tournaments and the leagues.
"Any suggestion of staging the World Cup at a time other than the traditional period is a crucial issue for the European Leagues considering the impact on the organization of domestic championships throughout Europe, and of the international football calendar around the world.
"The EPFL is of the view that no hasty decision shall be made by the FIFA executive committee of October 3-4."
The statement adds "such an important decision cannot be rushed with artificial deadlines" and says that a proper medical assessment on the impact of the heat on players and supporters should take place.
The EPFL also want FIFA to look at the consequences a move may have on the transfer system, any effects on commercial and media contracts and possible effects on the amateur game.
Blatter has also admitted for the first time that FIFA may have made a mistake when appointing Qatar as the host nation.
When it was suggested FIFA should have been aware that Qatar's climate would prevent a summer tournament taking place before they were voted as 2022 host in 2010, Blatter said: "That may well be so, and it may well be that we made a mistake at the time."
In an interview by insideworldfootball.com Blatter added: "On the other hand, you must also consider political and geo-political realities. The World Cup is FIFA's biggest, if not only, global event. Who are we, the Europeans, to demand that this event has to cater to the needs of 800 million Europeans above all?
"I think it is high time that Europe starts to understand that we do not rule the world anymore, and that some former European imperial powers can no longer impress their will on to others in faraway places.
"We must accept that football has moved away from being a European and South American sport, it has become the world sport that billions of fans are excitedly following every week, everywhere in the world."
Regarding proposals to switch the event to winter, he said: "After many discussions, deliberations and critical review of the entire matter, I came to the conclusion that playing the World Cup in the heat of Qatar's summer was simply not a responsible thing to do."
