Roberts said, "First and foremost, I'm pretty devastated to be missing this weekend's Heineken Cup quarter final match against Leinster, in what is our biggest match of the season."
"It's a match I've been looking forward to for a long time but unfortunately my body hasn't quite allowed me to be a part of such a huge occasion for us as a region. I originally injured my knee in Paris playing against Racing Metro after returning from the World Cup."
"With the fantastic help from the medical staff at the Blues and Welsh Rugby Union, I was able to rehab my knee well enough to get me through a handful of games for the Blues and the successful Grand Slam Six Nations campaign with Wales."
"However, following my injury in the match against Glasgow on Friday night I've been advised by the knee surgeon that my knee is now not stable enough to continue playing and potentially risk further injury to the knee."
"The decision has been made for me to have an operation on the Anterior Cruciate Ligament (ACL) later this week."
"It will mean a minimum of roughly 6 months away from the playing field. I suppose it's a chance for me to get my body fully right for what is a huge season for both club and country, with a certain carrot at the end of it too.
"It will also allow me to continue my focus on the final year of my degree in medicine and the finals I'll be sitting next March."