The injury is not, however, career-threatening and the Top 14 giants are hopeful the full-back will be back playing again this season.
Clermont, who lead Leinster by eight points in their pool with two games remaining, said that they would know more about the length of time he would be absent once the 32-year-old undergoes further tests.
"He suffered a broken bone in his fifth vertebra," the club said on their website.
"The length of his unavailability will be ascertained in the coming days by complementary examinations but we will not be seeing Lee Byrne again until at least the beginning of 2013."
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.