Ireland wing Tommy Bowe is set to miss this season's entire RBS 6 Nations Championship after undergoing knee surgery.
Bowe was carried off during Ulster's Heineken Cup home defeat against Northampton last Saturday.
In a statement, Ulster said: "Tommy Bowe has undergone successful surgery on his knee and is now expected to be out for approximately four months. The winger sustained significant lateral ligament damage to his right knee in the closing stages of Ulster's 10-9 Heineken Cup loss to Northampton."
Ireland launch their Six Nations campaign against defending champions Wales in Cardiff on February 2, before hosting England eight days later.
Bowe, who has scored 26 tries in 51 Tests, should regain full fitness ahead of the British and Irish Lions tour to Australia.