Ulster and Ireland wing Tommy Bowe could miss the Six Nations after suffering a knee injury during Saturday's Heineken Cup defeat to Northampton at Ravenhill.
The 28-year-old has sustained significant lateral ligament damage to his right knee and will undergo surgery in the next few days to repair the damage.
Bowe, a leading contender for the Lions squad, was hurt when he landed awkwardly following an attempted tackle by Jamie Elliott in the closing stages of the game.
An Ulster statement read: "At this stage it is not possible to put a timescale on how long his recovery period will be.
"A further update on this will be issued following the surgery, when the full extent of the injury will be known."
Bowe later tweeted: "Thanks to everyone for the messages. Will have surgery this week on my knee, it's not as bad as I feared so hopefully be back soon."
Ireland kick off this season's Six Nations tournament against defending champions Wales in Cardiff on 2 February.
Ulster second row Dan Tuohy suffered a calf injury against the Saints and will be assessed on Monday morning, along with fly-half Paddy Jackson, who sustained a dead leg midway through the second half.