Henderson, 26, sustained the injury in Ulster's European win over Leicester on Saturday and the province says he is likely to be out "for several weeks".

Ulster flanker Sean Reidy also requires hand surgery with number eight Marcell Coetzee to undergo a hamstring scan.

Munster lock Tadhg Beirne was ruled out of the Ireland squad earlier on Monday.

Beirne's knee injury led Joe Schmidt to call up Connacht's Quinn Roux to the Ireland squad.

Number eight Coetzee started in the Ulster back row alongside flanker Reidy in Saturday's 14-13 comeback win at Welford Road.

In addition, Ulster fly-half Billy Burns was concussed in Saturday's game and will follow the return to play protocols.

Henderson's finger injury is unrelated to the thumb injury which kept him out for a number of weeks before he returned to produce a man-of-the-match display in Ulster's Leicester win.

Ireland start the defence of their Six Nations campaign at home to England on 2 February before taking on Scotland away a week later.

After a one-week break, the holders will be away to Italy in Rome on 24 February before their concluding games at home to France and away to Wales on 10 and 16 March.

Ulster coach Dan McFarland will be hoping that Henderson is back to full fitness well before the province's all-Irish Champions Cup quarter-final against Leinster on the final weekend in March.

Henderson would have been expected to sit out Ulster's Pro14 games before that because of his Ireland involvement.

Ulster face Benetton on Friday night with Reidy certain to miss out and Coetzee and Burns also looking major fitness doubts.