Football League clubs have been assured they will be able to call on players involved in the 2006 World Cup finals for the end-of-season play-offs.
Andy Johnson will be unable to help Palace if he is on England duty
A Fifa ruling bars those picked for the World Cup from playing after 15 May, ruling them out of the play-off finals.
But a Football League spokesman said: "The FA has assured us there is an understanding in place with Fifa that will enable players to play.
"We are confident that this issue will be resolved."
The Championship play-off final is due to take place on 21 May, with the League One and Two finales a week later.
If Fifa stands by its ruling, Andy Johnson, if chosen by England, would miss the Championship final - if Crystal Palace reached it.
Players involved in the Champions League final on 17 May are already exempt.
Reading, Leeds, Southampton, Port Vale and Wrexham could also be affected.
Respectively the quartet have players representing the United States, Sweden and Trinidad and Tobago.
Fifa have introduced the cut-off date so players can have sufficient rest before the finals start on 9 June.
As well as moving the Champions League final, the Uefa Cup final has also been brought forward a week to 10 May.
"We don't want burned-out players. They will be free from other engagements," said Fifa general secretary Urs Linsi.
"The 23 players on the list for each of the 32 participating nations will not be available for any other competitions after this date.
"The Champions League final is a special exception."
There have been complaints in recent major tournaments that players involved in the major European leagues had arrived in an exhausted state because of the heavy schedule of matches during the domestic season.