Teams taking part in the new Club World Cup in June-July next year will be allowed to replace players during the tournament if the transfer window in their country is open at the time, world football's governing body Fifa said on Thursday.
Fifa member associations of participating clubs will also have the option of opening an "exceptional registration window" in June before the event begins to sign players.
The Club World Cup in the United States is scheduled to run from 15 June - 13 July but that period either coincides with ongoing leagues where the transfer window is closed or countries where the window is open and player contracts end.
Fifa said the optional window for member associations will be open from 1-10 June "for all their affiliated clubs" before the tournament gets under way in a bid to make it fair for all clubs in the league to sign players during the same period.
"The decision as to whether or not to open an additional window remains at the full discretion of each Fifa Member Association concerned," Fifa said in a statement.
With most player contracts expiring on 30 June, Fifa also said participating clubs may replace players during a "restricted in-competition period" from 27 June - 3 July.
But a standard registration window - like the summer one in Europe -- must be open for the club at the time.
Players who start the Club World Cup with one team cannot play for another side in the tournament if they switch.
The 32-team Club World Cup includes 12 European sides with players whose deals may finish at the end of their season.
"The objective is to encourage clubs and players whose contracts are expiring to find an appropriate solution to facilitate the players' participation," Fifa added.