Munster have received a boost ahead of their European Champions Cup semi-final against Saracens with the return of CJ Stander, but Sean O'Brien will miss Leinster's clash versus Clermont Auvergne.
Stander sustained an ankle injury in his side's quarter-final victory over Toulouse and missed subsequent Pro12 triumphs against Glasgow Warriors and Ulster.
However, the Ireland international - named in Warren Gatland's 41-man British and Irish Lions squad on Wednesday - is in the starting XV to face Saracens at Aviva Stadium on Saturday.
The match comes too soon for fellow Lions pick Conor Murray, however. The scrum-half has been absent with a shoulder issue since March and Gatland suggested Murray could lose his place on the tour to New Zealand if he does not return before the end of the season.
Saracens' starting XV features all six of their Lions representatives: Owen Farrell, Maro Itoje, Billy Vunipola, Mako Vunipola, Jamie George and George Kruis.
Leinster have suffered a blow ahead of their semi-final against Clermont, with O'Brien ruled out due to hamstring tightness. The Lions back-rower will be reassessed before next Friday's Pro12 clash with Glasgow Warriors.
David Strettle replaces Noa Nakaitaci (ruptured anterior cruciate ligament) in the only change to Clermont's quarter-final line-up, after Davit Zirakashvili, Benjamin Kayser and Sebastien Vahaamahina were all passed fit.