Toulouse centre Sofiane Guitoune has been ruled out for the rest of the season, the Top 14 club announced on Tuesday, after tearing the anterior ligament of his left knee during the weekend defeat by Montpellier.
The France midfielder, who suffered the injury on his 32nd birthday on Saturday, had only just returned to action after another injury had kept him out for two months.
It is a major blow for Toulouse ahead of Saturday's European Champions Cup last 16 match at Munster.
They are already without wingers Lucas Tauzin and Juan Mallia, full-back Thomas Ramos and centre Pierre Fouyssac while Pita Ahki is also doubtful because of an Achilles tendon problem.
In their absence, coach Ugo Mola may be forced to pair Australian fly-half Zack Holmes and the relatively inexperienced Dimitri Delibes in midfield in Limerick.
There is also some uncertainty over winger Yoann Huget, who is also suffering from an Achilles tendon injury.
Second row Joe Tekori, meanwhile, faces a disciplinary hearing on Wednesday after being cited for an incident in the match against Montpellier.
The only good news is the return of former New Zealand forward Jerome Kaino who has been sidelined with an elbow injury since the end of February.
The likes of Romain Ntamack, Antoine Dupont and Julien Marchand are set to feature at Thomond Park after playing for Les Bleus during the Six Nations campaign.