But the pair are recovering ahead of schedule and could play for the Blues in Saturday's PRO12 clash with Munster at Musgrave Park in Cork.
"We haven't seen Jamie or Leigh around for a while, but they have both pushed themselves back into contention," said Blues backs coach Gareth Baber.
"They are going through some tests this week just to make sure they are given the all-clear.
"But we expect to see them involved this weekend."
Roberts, who was named HSBC Player of the Tour when the Lions travelled to South Africa four years ago, confirmed he is hoping to be back involved for the first game of the new year having sat out the last nine regional fixtures.
"I am fortunate to be back a week early and that is testimony to the physios," said Roberts.
"You get given guidelines from injuries and I was looking at six weeks after tearing some ligaments but not requiring surgery.
"I am raring to go in what is a really big season and cannot wait to get back into action.
"It has been a frustrating campaign because I have suffered niggling injuries and I just want to stay fit.
"I got knocked out against Argentina and took a knock to the hip against New Zealand where I could not run and that was followed by the elbow injury in the Australia game.
"It has been frustrating, but I can't dwell on events because these things happen in rugby."
Like Roberts, Halfpenny picked up his injury in Wales' last-minute defeat to Australia on December 1.
Halfpenny suffered the setback in the process of attempting to prevent Kurtley Beale's match-winning score but he now looks set to return to the Millennium Stadium against the Irish when Wales kick off the defence of their Grand Slam in a month's time.