Gloucester scrum-half Haydn Thomas will be out for six weeks after fracturing his collarbone in the European Challenge Cup win over Bayonne.
The 23-year-old, who had made 11 appearances this season, was on as a replacement when he was injured.
"It's disappointing because he had been pushing for an opportunity," coach Dean Ryan told the club website.
"With the Six Nations upon us he had a real chance to press that claim but unfortunately that won't happen now."
Gloucester's two other first choice scrum-halves, Peter Richards and Simon Amor, are away this week with the England senior and sevens squads respectively.