Ireland coach Eddie O'Sullivan was this morning counting the cost of a bruising Heineken Cup weekend that forced three injured players to pull out of his squad for the start of the Six Nations next week.

Leinster wing Shane Horgan, one of Ireland's most influential players in recent seasons, underwent surgery yesterday for a knee injury suffered against Gloucester on Friday, and will need up to six weeks to recover.

He will be joined on the sidelines by Leinster teammate Robert Kearney, suffering a hamstring strain, and Munster's John Kelly, who picked up a rib injury during Munster's defeat at the hands of Leicester.

All three will miss the opening clash with Wales in Cardiff on Sunday week with Horgan almost certain to miss the back-to-back visits of France and England to Croke Park.

Malcolm O'Kelly, who came off on Friday with a recurrence of a previous knee problem, was being assessed by doctors today.

The three injuries, plus a number of further knocks sustained over the weekend, forced O'Sullivan to cancel a training session this morning as he prepares for a tilt at the championship.

"The squad have picked up a couple of knocks at the weekend," said O'Sullivan. "It was in the best interests of the players to prioritise rehab and recovery today to allow us to hit the ground running tomorrow."

In place of the injured trio, O'Sullivan has called in Connacht's Danny Riordan, Leinster's Kieran Lewis and Northampton's David Quinlan to the 35-man squad.