Ireland forward Tadhg Beirne will miss the opening two matches of the Six Nations due to a knee injury, Irish Rugby Football Union confirmed on Monday.
Scotland have included four new players into their Six Nations squad but flanker Hamish Wilson has withdrawn due to a hand injury.
Flanker Brad Shields has become the latest injury concern for England ahead of the Six Nations after he was ruled out of Wasps' European Champions Cup clash with Leinster.
Dylan Hartley has been left out of England's Six Nations squad due to injury as Eddie Jones included four uncapped players in his 35-man group.
Injuries to key players forced Scotland coach Gregor Townsend to select seven uncapped players in his 39-man squad for the Six Nations.
Wales included Leigh Halfpenny in their Six Nations squad on Tuesday, despite the fullback having not played rugby since he was concussed against Australia in November.