Group leaders Ospreys are without injured Wales lock Ian Gough for their EDF Energy Cup trip to Harlequins on Sunday, while Ryan Jones' return from a shoulder injury has been postponed.

Group C - Harlequins v Ospreys (15:10)

The Welsh outfit, who top the pool by five points from the Quins, need just one match point or must prevent Harlequins picking up a maximum five-point haul to book their place in Sunday's semi-final draw.

It would also make them the only club from Wales in the final four after Wasps, Saracens and defending champions Leicester secured the first three spots on Saturday.

Gough has not recovered from a sternum injury suffered against Gloucester in the Heineken Cup while Ryan Jones' comeback from a long-term shoulder problem has been delayed.

Gough should be available for selection next week though Ryan Jones is hoping for a return by the end of December.

Paul James starts at prop for the Ospreys ahead of Duncan Jones while Mark Taylor comes in at inside centre in place of Wales international Sonny Parker.

Mike Phillips starts at scrum-half ahead of Justin Marshall, who was named on the bench after playing for the Barbarians duty on Saturday, and forms a half-back pairing with James Hook (pictured).

Harlequins director of rugby Dean Richards makes two changes to his starting XV. Adrian Jarvis replaces injured Chris Malone at fly-half while Will Skinner comes in for Paul Volley on the openside flank.

Richards keeps the pack unchanged while Chris Hala'ufia and Jim Evans have recovered from illness to take their places on the bench.

Group C - London Irish v Worcester (15:00)

Argentine centre Gonzalo Tiesi makes his debut for London Irish in this dead rubber.

Irish are bottom of the group with no wins from two games while Worcester's one victory leaves them with too much to catch up to secure a spot in the semi-finals.

The Exiles pack is bolstered by All Black prop Clarke Dermody, who makes his second start after recovering from injury.

Irish director of rugby Brian Smith has given a number of young players the chance to prove themselves, including wing Dominic Shabbo and centre Nils Mordt.

Smith's counterpart Mike Ruddock has also gone for youth and fly-half Joe Carlisle gets a start after impressing in the A league this season.

New Zealand lock Greg Rawlinson is handed a full debut, while prop Matt Mullan is handed his first start.

James Collins is named on the flank in a back row that includes Netani Talei at blindside and Kai Horstmann at number eight.

Group D - Bristol v Leeds Carnegie (15:00)

Bristol head coach Richard Hill has rung the changes for the clash with Leeds, selecting a number of younger players as the club has no chance of reaching the knock-out stages.

Up front, prop Ray Hogan is set to make his first competitive start alongside David Blaney and Darren Crompton.

In the back five, young prospects Dave Attwood, Redford Pennycook and James Phillips feature with veteran Gareth Llewellyn and the experienced Matt Salter.

Leeds' academy wing Scott Armstrong is set to make his full debut after scoring off the bench in their clash with Saracens earlier in the competition.

Andy Boyd, also from the academy, starts on the bench for a side captained by Joe Bedford.

Scotland international flanker Jon Dunbar returns after tearing a hamstring in Leeds' second game of the season.

Terence O'Rorke / Eurosport