A scan on Keith Earls today in Limerick confirmed he has sustained medial ligament damage and will be out of action for between four and six weeks.
Earlier, it was confirmed that Ireland captain Brian O'Driscoll faces surgery for a trapped nerve and will be out of action for up to six months.
O'Driscoll said the problem probably goes back to the Six Nations. He struggled with a shoulder problem throughout the World Cup and missed Friday’s RaboDirect PRO12 game against Munster.
"It comes at different times..There's a jolt factor with a stinging sensation. It's not just a case of dealing with the pain factor - it's when you lose power, you're not much use to your teammates for the three minutes or so until it comes back," he said.