UEFA has been warned it will lose billions if the World Cup is held every two years.
French media outlet Le Monde says an independent report commissioned by UEFA claimed the European soccer body would lose 3 billion euro ($A4.7 billion) over four years if FIFA's proposed new calendar was introduced.
Le Monde said the study conducted by London-based Oliver & Ohlbaum Associates was commissioned in September and the findings were revealed to their 55 national associations on Tuesday.
Proposals led by former Arsenal manager Arsene Wenger, now FIFA's chief of global football development, look set to re-shape the international football calendar.
FIFA's plans include a men's tournament every June, mandatory 25-day rest periods for players after their involvement in tournaments, and cutting the number of qualifying matches and the number of international breaks during a season.
Closing the gap between World Cups from four years to two, however, has been met with widespread opposition, including from the International Olympic Committee.
The change in schedule would see the confederation tournaments - such as the European Championships and Copa America - also take place every two years, with qualifying matches condensed into either one window or two, thereby cutting the number of international breaks and related travel.
UEFA's study showed this was where the risk to revenues would impact most, with 2.5bn euro ($A3.9 billion) losses incurred if there were two international windows in October and March and 3 billion euro if a single window was adopted over a four-year cycle.
The deficit would be mainly related to income from match tickets, broadcasting revenue and sponsorship, with some deals already contracted under the current structure.
The independent study also examined the impact of both mental fatigue for players and a lack of competition for some of nations, who if they fail to qualify for the final stages could be without an international fixture for as long as six months.
It also suggested women's football would lose standing, as the showpiece events would conflict against men's tournaments as well as the Olympic Games, while the study concluded there would be a "domino effect" on domestic competitions across UEFA.
Australian Associated Press