Ulster Rugby has launched an investigation into the "alleged unauthorised absence" of backrow forward Nick Williams and say the New Zealander will not play a part in Friday night's game Newport Gwent Dragons at Ravenhill.

Williams returned to New Zealand for what were described as personal reasons and missed last Sunday’s victory over Treviso in Italy. The 30-year-old is reported to have returned to Belfast.

Prop John Afoa also travelled home to New Zealand due to a family bereavement.

A key part of the Ulster set-up since joining the province in the summer of 2012, Williams signed a contract extension last October that will keep him at Ravenhill until the summer of 2016.

A brief statement from Ulster Rugby read: “Nick Williams is unavailable for selection for Friday night’s match against Newport Gwent Dragons due to an internal investigation into alleged unauthorised absence. Ulster Rugby will make no further comment on the matter at this time.”