Roberts suffered ligament damage in that domestic clash but had been expected to return to action in time for Wales' trip to Dublin on February 4.
But Blues boss Gareth Baber has admitted his midfield maestro won't be available for next Sunday's Heineken Cup tie with Racing Metro and is touch and go to be on the plane to Dublin a week later.
"I think it's possibly all come a bit too soon for Jamie," said Baber after the Blues beat London Irish 22-15 in Reading.
"You never quite know and you hope it's going to clear up quite quickly but I don't think it's going to be good for Jamie this week.
"I'm not entirely sure what the take is going to be on Jamie going off with Wales. He's obviously been recovering from this leg injury…we'll have to have look this week."
Losing Roberts would be a big blow for Warren Gatland's World Cup semi-finalists.
The HSBC Man of the Tour when the Lions headed to South Africa in 2009 looked to be back to his best during the global gathering in New Zealand.
But his absence could be positive news for another Cardiff Blues Lion in Gavin Henson. The 2005 tourist started yesterday's European fixture at inside centre and could now be in line for a Wales spot alongside Jonathan Davies, Ashley Beck or Scott Williams.
Henson came close to a shock World Cup call up before injuring his wrist in the Millennium Stadium win over England and has since featured twice at full back for his new club before his first outing back in midfield.
"We saw a couple of little bits of class that come from Gavin - a pass and a half break when he could possibly have linked up with Leigh Halfpenny on a short ball," added Baber.
"He's got that vision and that skill level and you want to try and involve that as much as you can in a game.
"He wants to be involved closer to the ball and closer to the action. I thought he looked more comfortable than he did in the Ospreys game when he played full back. He was very critical of himself when we spoke after that Ospreys match."