Hamstrung Davis out of Romania qualifier
The Southampton midfielder suffered the injury in last Saturday's 2-0 Premier League victory over Leicester City.
Davis reported for international duty on Tuesday, but the Irish Football Association announced on Wednesdasy that the former Rangers man will miss the Group F clash in Bucharest.
The 29-year-old's absence is a big Michael O'Neill's side, who are top of the group after winning all three of their qualifying games so far.
Second-placed Romania will leapfrog Northern Ireland if they secure all three points on Friday.