Ulster's preparations for their crucial Challenge Cup quarter-final against La Rochelle this Friday (20:00 BST) have hit a potential snag, with two key players facing a race against time to be fit.

Hooker Rob Herring and scrum-half Nathan Doak are both considered injury doubts after picking up knocks in the side's hard-fought 28-24 victory over Ospreys this past Saturday. Herring is managing a calf issue, while Doak is battling an ankle problem.

The injury list doesn't end there for head coach Richie Murphy. The province has confirmed that Stewart Moore (knee), Rory McGuire (shoulder), James McNabney (knee), Michael Lowry (groin), and Robert Baloucoune (elbow) will all remain unavailable for selection this weekend, testing the squad's depth.

Despite the setbacks, Ulster will look to build on their recent momentum, entering the knockout clash unbeaten in their last two outings. Standing in their way for a semi-final spot, however, is a formidable La Rochelle side. The French giants secured their quarter-final berth with an 18-26 win over Newcastle Red Bulls and have been in strong form, winning three of their last four matches.

Elsewhere in the Challenge Cup quarter-finals, Montpellier host Connacht, Benetton welcome Exeter Chiefs, and Zebre face the Dragons in what promises to be a thrilling weekend of European rugby.