The Scotland stand-off damaged his groin in the first half of Scotland’s win over Wales in Llanelli in October. His replacement, Adam Hastings, injured his shoulder in the second half and the visitors finished the match with Stuart Hogg at stand-off.
The fear was that Scotland could be without both their first-choice fly-halves for the start of the Six Nations but Russell’s return is a huge boost for club and country.
Gregor Townsend’s side open the championship away to England on February 6.
Russell’s appearance against Wales was his first start for Scotland since falling out with Townsend on the even of last season’s Six Nations.
The pair have since repaired their relationship and Townsend will welcome the earlier than expected return of arguably Scotland’s most creative player.
Racing, who were beaten finalists last season, host Connacht at the Paris La Defense Arena on Sunday.