The Munster man is being brought in as injury cover
Tomás O'Leary is headed to France to join Top 14 side Montpellier on a short-term deal.
Scrum-half for the French side, Benoit Paillaugue, has been ruled out for several months through injury and the French club have turned to the experienced Corkman as an able deputy, who has joined as a "medical joker."
O'Leary's deal is for three months, which is the minimum allowed for short-term injury cover under ERC rules, and will still be settling into the squad when they travel to Leinster in the Champions Cup on the weekend.
The Challenge Cup holders will be hoping that they can make amends for their loss last weekend, when they conceded a late penalty against Northampton Saints, surrendering their 14-13 lead with almost no time left on the clock.
In the wake of that defeat, head coach Jake White remained positive, however, stating that his side were used to adversity and that they wouldn't be thrown off their rhythm as a result.
"We gave two penalties away in the last 90 seconds which wasn't good," said White, "but we get to play them again. Last year we lost our first game to Harlequins and went on to win the competition. Stranger things have happened in sport."
O'Leary will be keen to feature in a Champions Cup side, having been used sparingly by Munster this season, with just two appearances to his name.