Ireland captain Johnny Sexton was due to undergo surgery on Tuesday after suffering a cheekbone injury.
Fly-half Sexton was hurt during Leinster’s United Rugby Championship victory over Connacht in Dublin on Sunday.
The 37-year-old has been ruled out of next weekend’s URC clash against the Ospreys – and could now be a doubt for the start of Ireland’s Six Nations campaign.
“Sexton suffered a cheekbone injury during the game against Connacht Rugby and will have a procedure today and will be further assessed then,” Leinster said in a statement posted on their website.
Ireland, the world-ranked number one team, visit Wales for their Six Nations opener on February 4.
Andy Farrell’s side then have a potential title-defining appointment with France in Dublin seven days later.
Sexton, who has won 109 caps, missed two of Ireland’s three Autumn Internationals this season because of injury.