The 26-year-old Wales centre, who moved to Racing from the Blues after starring for the British & Irish Lions in the summer, suffered the setback in the Top 14 win over Perpignan on September 9 and hasn't played since.
Roberts has now had surgery to correct the problem and is therefore destined to miss at least the first two pool games of the continent's premier club competition.
"Jamie's had an operation on his ankle and he's going to be out for about two months," said Racing Metro coach Laurent Labit.
"He was very keen to play for us at the start of the season but he came back from the Lions tour quite tired. It's been a big year for him with the Lions and finishing his medical studies so I think he was probably a bit mentally tired as well.
"Hopefully he will be back to his best for the second half of the season."
A two-month absence would prevent Roberts from featuring against fellow French giants ASM Clermont Auvergne on October 13 and the trip to the Scarlets six days later.
Labit is hopeful one of his star men will be back in time for the double header with former Amlin Challenge Cup winners Harlequins on December 7 and 15, though, as Racing aim to get out of the group stages for the very first time.
Racing won three of their six Heineken Cup fixtures last season and were looking good for a quarter-final spot before losing to Saracens in front of more than 35,000 fans in Nantes in Round 5. A convincing defeat to Munster followed on the final weekend of action as they finished third in Pool 1.