Ireland head coach Joe Schmidt expects Johnny Sexton to be available for their Six Nations opener against England.
Second rows Iain Henderson and Tadhg Beirne are both unlikely to be fit until the visit of France on 10 March.
Sexton, 33, has not played since Leinster's Pro14 derby loss to Munster on 29 December because of a knee injury but he returned to training this week.
"He'll train fully on Thursday and we will then ramp up his training," said Schmidt.
"Our expectation is that he will get through it without any problems. Johnny is confident and the medical staff are confident."
Henderson and Beirne will both be sidelined until after the second rest week of the tournament but Ireland are hopeful they will both be available for the penultimate round match against France at the Aviva Stadium.
Henderson sustained a finger injury in Ulster's European Champions Cup win at Leicester and is likely to be out of action "for several weeks" while Beirne is struggling with a knee injury, which has forced Schmidt to add Connacht lock Quinn Roux to his training squad.
The injuries to the pair leave Schmidt with just four fully fit second rows to choose from for the opening match against England on 2 February with Roux and his Connacht teammate Ultan Dillane providing competition for Leinster's James Ryan and Devin Toner.
Ireland could overtake New Zealand as the top-ranked side in the world during this year's Six Nations but Schmidt says it will be difficult for his side to retain the title they won last season.
"I don't think we are clear favourites," the Ireland coach added.
"The psyche is one of enormous respect. You know if you don't get things right, England can get a long way away from you.
"They are a team back on an upwards swing, and they will be driven to rebound well from last year's Six Nations."
The Ireland and England squads are both holding warm-weather training camps in Portugal this week ahead of their opening-round meeting in Dublin.