Cameroon named uncapped Gaetan Bong and Eric Choupo-Moting in their 23-man World Cup squad on Saturday, even though the pair have yet to receive FIFA approval to play for the Indomitable Lions.
FIFA on Friday confirmed receipt of an application from Cameroon to use Bong and Choupo-Moting, previously capped at junior level by France and Germany respectively, but said the documentation was incomplete.
"We have already started the relevant investigations, however, to this day, the files are not yet complete and therefore we are in contact with the Cameroon Football Federation," a FIFA spokesman said.
"Cases can take different periods of time to review, dependent on the amount of information which is supplied by the respective FA, and how quickly."
Coach Paul Le Guen named German-born Marcel Ndjeng on stand-by in case FIFA turn down the application by either Bong or Choupo-Moting.
Le Guen included Vincent Aboubakar from Coton Sport in his final 23, a rare run for the home-based player at a major tournament for Cameroon.
Long-serving defender Rigobert Song will play in a fourth World Cup tournament, having debuted as a teenager in the United States in 1994.
Cameroon are in Group E for the June 11 to July 11 tournament, with the Netherlands, Denmark and Japan.