The 24-year-old, whose second half try in Marseille helped the Blues lift the Amlin Challenge Cup with victory over Toulon in May, has been forced to watch from the sideline as the Blues' began their Heineken Cup campaign this year.
The Blues put in a strong performance at home against Edinburgh in the opening fixture but slipped to defeat away to Castres in Round 2. Whilst Roberts will miss the back-to-back games against former European Champions Northampton later this month he should be fit for the remaining two pool games in January.
"Jamie's comeback won't be too long after Christmas," said Young.
"He's getting there and has another appointment with the specialist in a couple of weeks. We will then pinpoint a game for him to return."