Roberts needs surgery, misses Oz tour
It will mean a minimum of roughly six months away from the playing field," he said in a statement from his club side Cardiff Blues.
"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."
His injury is also a blow to the Blues, who sacked former Wales player and fellow centre Gavin Henson on Monday following a drinking incident on a flight.
They visit Ireland's defending champions Leinster in a Heineken Cup quarter-final this weekend.