Ndidi was injured during his club Leicester City’s 2-0 win at Cardiff City on December 29th, although details of the injury were not made clear by either his club or Nigeria.
Leicester teammate Kelechi Iheanacho (27) is also struggling with injury but was still being assessed at Nigeria’s training camp in Abu Dhabi, the federation added in a statement.
Iheanacho had missed the last two matches for his club, who are runaway leaders in the Championship in England.
Yusuf is uncapped but helped Royal Antwerp to the Belgian league title last season and competed in all their Champions League group matches between September and December.
Nigeria open their Cup of Nations campaign on January 14th with a Group A game against Equatorial Guinea. They also meet hosts Ivory Coast and Guinea Bissau in their group matches.