Both sides picked up narrow wins in Round 4, with Ulster beating ASM Clermont Auvergne 34-31 and Harlequins edging out Castres Olympique 36-33 to seal second-place finishes in Pool B and Pool A respectively.

Ulster now host Scarlets in the United Rugby Championship, with the Welsh region having dropped out of European competition after finishing bottom of Pool B.

With a contingent of players joining up with Ireland ahead of the Six Nations Championship, the Irish province have made six alterations to the side who started against Clermont last Saturday.

Rob Lyttle and Craig Gilroy start on the wings, with Ethan McIlroy switching to full-back, while Ben Moxham comes in at centre. Flanker Greg Jones, lock Sam Carter and hooker John Andrew have also been brought in.

Meanwhile, Quins, also depleted by international call-ups, make six changes too for their Gallagher Premiership visit to Bath Rugby, whose 11th place finish in Pool A has seen them drop into the EPCR Challenge Cup.

A new-look front row sees Santiago Garcia Botta and Will Collier start either side of hooker Jack Walker, while Matt Symons returns at lock, with Dino Lamb shifting to flanker and Viliami Taulani at No.8.

Danny Care and Tyrone Green are restored at scrum-half and full-back respectively, with fly-half Tommy Allan also coming in.

Ulster Rugby and Harlequins are both forced to make changes for their return to domestic action on Friday night following the conclusion of the Heineken Champions Cup pool stage last weekend.