London Irish have confirmed that scrum-half Tomas O'Leary has undergone a surgical procedure on his lower back.

The 29-year-old has been out of action since suffering the injury against Harlequins at the end of October, but it had been suggested that he would return in January.

However, he underwent the operation last Tuesday on the pre-existing injury and will therefore miss the next four to six months of the season.

O'Leary has made 24 international appearances for Ireland.