The veteran fly-half has been included in a 37-man training squad for the penultimate round of the Championship, taking place this weekend.
The 37-year-old Leinster playmaker, who has toured twice with the British and Irish Lions, is expected to come in for Ross Byrne, who started the 34-20 victory over Italy, after struggling with a groin injury.
Scrum-half Jamison Gibson-Park, prop Tadhg Furlong and centre Robbie Henshaw are also in the squad following spells in the treatment room.
Ireland have beaten Wales, holders France and Italy as they chase their first Grand Slam since 2018, with matches against Scotland and England to come.
Glasgow quartet Simon Berghan, Scott Cummings, Rory Darge and Stafford McDowall have been added to Gregor Townsend's Scotland squad for the match at Murrayfield.
Suspended Grant Gilchrist, who misses the rest of the campaign after being handed a ban following his red card against France, has returned to Edinburgh and Josh Bayliss has returned to Bath.
Scotland won their first two matches of the Six Nations, against England and Wales, but lost 32-21 in Paris late last month.
