Newcastle and Millwall could face FIFA sanctions over the unavailability of Shola Ameobi and Danny Shittu for Nigeria's African Nations Cup.
Ameobi and Shittu are both expected to reject call-ups for the tournament and have angered their country's football federation with their decisions.
Newcastle manager Alan Pardew has said Ameobi will not be appearing in the tournament, which begins on January 19, while Millwall defender Shittu is also expected to reject a call-up should one come.
FIFA rules state that any player who doesn't report for international duty when called up can be made ineligible for the period of their proposed call-up, with an additional five-day extension possible in certain circumstances unless a prior agreement is struck between club and country.
And Nigeria Football Federation board member Chris Green told BBC Sport that they would be willing to pursue punishment for the clubs if they don't release their players for international duty.
He said: "These clubs are not only disrespecting Nigeria but FIFA and CAF (Confederation of African Football) as well.
"The rules are clear on international games approved by FIFA so we consider these comments (by Newcastle and Millwall) as not only ridiculous but totally disrespectful.
"We know the rules. FIFA has made it clear that these clubs will not be able to use these players for the duration of the Nations Cup plus an additional five days.
"We will further push for additional sanctions - we understand these clubs employ our players but they are also international footballers. Rules are rules. Newcastle and Millwall must understand the basics why they exist."
Information from the Press Association was used in this report.