Roberts, who played on for more than 10 minutes after the injury, has progessed well so far and could now be in line for a return to action by the middle of next month.
"I started back in training on Monday, just doing light stuff," said Roberts.
"I can't put any strain on the injury, so I can't lift any heavy weights, but I can do fitness work and light weights to keep the muscles ticking over."
The Blues currently top Pool 6 of the Heineken Cup after four successive European wins and Roberts is hoping to be back involved by the time the competition starts again early next year.
"I'm seeing a specialist at the end of December and then fingers crossed I'll be back playing in the middle of January, which is six weeks after the injury. That's the usual time for a fracture to heal and this is no different really.
"We've got Gloucester on January 18 and Calvisano the week after, which are two massive games which I'd love to be involved in.
"Hopefully, by the end of next week I'll be back up there fitness wise and just looking to add the muscle and strength which I've lost. I've just got to knuckle down in training and get myself in the frame."