The 29-year-old limped off in the first half of Munster's Heineken Cup clash against Castres last Saturday and scans this week have revealed damage to a cruciate ligament.
He will now undergo surgery on February 3 to repair the damage and look to resume playing next season.
Ronan joins fellow flankers David Wallace and Tommy O'Donnell in the Munster rehab room although good news for the former European champions is that both are expected to return to training over the course of the next month.
Meanwhile, reports in the Irish press suggest that Munster are hoping to sign a new centre duo with Northampton Saints' James Downey and Cardiff Blues' Casey Laulala believed to be on the shopping list as the Irish giants prepare for the departure of Will Chambers.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.