Arsenal are set for a row with the Nigerian FA after refusing to allow Kanu to join up with his national squad. Gunners boss Arsene Wenger will not allow Kanu to join Nigeria's pre-African Nations Cup training camp until after 18 January.
That meets Fifa's rules, but Nigeria claim they have an agreement over the release of players.
Wenger said: "Kanu is fit and doesn't need a pre-tournament camp."
The tournament kicks off in Tunisia on 24 January, but the Nigerians gather for their training camp on 11 January.
Fifa rules require clubs to allow players to report for international duty six days before games.
Arsenal are without Sylvain Wiltord and Dennis Bergkamp for at least 10 days through injury, and Wenger said: "We want Kanu to play here for as long as possible."
But Nigerian FA spokesman Samuel Kaalu insisted: "We have an understanding with the clubs that they will let players report for the camp.
"We expect them to respect that gentleman's agreement.
"If the players aren't released then we'll look at the situation urgently and will do everything to ensure that they are.
"The African Nations Cup is as important as the European Championships are to Europe and we expect European clubs to respect it."
Arsenal's stand comes in the wake of Tottenham's row with striker Freddie Kanoute, who wants to play in the tournament for Mali.
Other Premiership clubs face a similar dilemma over the release of players.
Bolton expect Jay-Jay Okocha to join up with the Nigerian squad on January 16, while Celestine Babayaro has not yet told Chelsea when he wants to go.
Senegal expect Wolves striker Henri Camara to join their squad after Saturday's game against Charlton, but the Midlands club want him to play in the FA Cup replay against Kidderminster next Tuesday.