Ulster confirmed the New Zealand-born player is suffering from "severe trauma to the AC joint in his right shoulder with extensive soft tissue damage and bruising."
While the club were reluctant to pinpoint a comeback date it is thought Boss will be fit by the beginning of February.
Ireland will announce an extended squad for the Six Nations championship next week.
Peter Stringer is set remain first-choice scrum-half but should Boss fail to recover in time Ireland would have a tricky decision to choose a new understudy.
Kieran Campbell, Guy Easterby and Eoin Reddan are all previously capped at scrum-half and will look to impress in the run up to the Six Nations.