Yakubu has been left out of Everton’s squad for the home game against Reading on Saturday after failing to return on time from the Africa Cup on Nations.
The 25-year-old striker was expected at Everton’s training headquarters on Wednesday after Nigeria’s quarter-final defeat by hosts Ghana.
But he did not arrive until Friday and may face a club fine of a fortnight’s wages, estimated to be about £80,000.
He met with Everton boss David Moyes, who said: “All I would say is that it is an internal matter. Yak has been in this morning, I have spoken to him and he won’t be included in the squad for Saturday.”