New Ulster signing Alby Mathewson will be available for their Champions Cup quarter-final against Toulouse after organisers waived the cup-tied rule for this season.
The scrum-half has already played with Munster in the 2019/20 competition, and would normally not be eligible for another club in the same tournament.
However, due to the nature of the season, prolonged due to the coronavirus outbreak, European Professional Club Rugby (EPCR) has amended the rule.
"As a number of players have recently changed clubs, it has been decided on an exceptional basis to waive the rule which prohibits players from playing for different clubs in the same competition in the same season," it said.
"A player who has already been selected in a match day squad during the pool stage of this season’s Heineken Champions Cup or Challenge Cup will be eligible to play for his new club in the same competition during the knockout stage provided his registration is approved by EPCR and the relevant union."
That means that five-cap New Zealand international Mathewson will be available for Dan McFarland’s side’s daunting trip to Toulouse on 20 September, as will out-half Ian Madigan who moved from Bristol Bears during the break.
Ireland international Madigan played twice for the English club in the Challenge Cup.
Mathewson (34) would likely play as a back-up to first-choice scrum-half John Cooney.
The rule change did not affect Leinster as they didn’t add to their roster, while opponents Saracens have moved on a number of players.
EPCR will also allow any number of non-Europeans into a match-day squad, while there must be 12 front rows named in the extended panel, which must be registered by 1 September at the latest.
Follow Leinster v Munster (7.35pm, Saturday) and Connacht v Ulster (4.30pm, Sunday) via our live blogs on RTÉ.ie/sport and the News Now app, or listen to live commentary on RTÉ Radio 1