Centre Robbie Henshaw is unlikely to return to fitness before Ireland’s Six Nations opener against England on 2 February.
Leinster revealed on Monday the 25-year-old faces up to another eight weeks on the sidelines.
Henshaw picked up the hamstring injury during the warm-up for Ireland’s win over Argentina last month.
He missed the last three games of Ireland’s Grand Slam winning campaign with a dislocated shoulder.
The injury also rules him out of Leinster’s three remaining fixtures in Pool One of the European Champions Cup.
Henshaw has suffered a frustrating run of injuries having prematurely left the British and Irish Lions tour of New Zealand last year with a damaged pectoral muscle.
He returned to international duty the following February, featuring in Ireland’s win over France before injuring his shoulder while scoring his second try against Italy a week later.
Having been rested for Ireland’s opening autumn test against Italy, Henshaw was set to partner Garry Ringrose in midfield against Argentina.
Ulster’s Will Addison was drafted in as a late replacement following Henshaw’s warm-up injury, while Bundee Aki wore the number 12 jersey against New Zealand.
Ireland will begin the defence of their Six Nations title at home to England before taking on Scotland in Murrayfield a week later.