"Member associations of the clubs participating in the FIFA Club World Cup will have the option of opening an exceptional registration window from 1 to 10 June 2025 (for all their affiliated clubs) prior to the start of the competition," the body said in a statement following a FIFA Council meeting in Zurich.
"The decision as to whether or not to open an additional window remains at the full discretion of each FIFA member association concerned."
The extra window, which is in addition to those in January and over the European summer, would allow teams taking part in the Club World Cup to strengthen their squads before the tournament, which will run from June 15 to July 13 next year.
With June 30 the traditional date on which contracts expire, FIFA will also allow clubs to replace a limited number of players during a brief window within the competition, from June 27 to July 3.
"The objective is to encourage clubs and players whose contracts are expiring to find an appropriate solution to facilitate the players' participation," FIFA said.
Furthermore, FIFA is seeking to anticipate any potential conflicts related to the calendar due to the Club World Cup clashing with international tournaments.
The CONCACAF Gold Cup is due to be played at the same time in Canada and the USA, and so any player who could be involved in both tournaments will have the freedom to choose which one he wishes to play in.
Normally players are obliged to honour international call-ups.
The first edition of the expanded Club World Cup will feature 32 teams and will take place in the United States, with the final at the MetLife Stadium in East Rutherford, New Jersey, just outside New York City.
European participants will include Real Madrid, Manchester City, Bayern Munich, Chelsea and Inter Milan.
Other clubs from around the world to feature include Al Ahly, Boca Juniors, Flamengo, Palmeiras, River Plate and Mamelodi Sundowns.
