Ospreys host Harlequins at Brewery Field this Sunday with both teams still in with a chance of qualifying.
The home side must win and hope other results go their way; Harlequins need just two points to secure qualification.
Rhys Webb will skipper an Ospreys team that has been hit by injuries and international call-ups.
They do include Wales internationals Jonathan Thomas and five-time capped Kiwi Campbell Johnstone.
Rory Clegg returns at fly-half and Ross Chilsholm starts at fullback after coming back from injury last week.
Luke Wallace will lead the side as they aim for a home semi-final.
Ospreys: 15 Jamie Murphy, 14 Tom Grabham, 13 Jonathan Spratt, 12 Ben John, 11 Dafydd Howells, 10 Matthew Morgan, 9 Rhys Webb (c), 8 Morgan Allen, 7 Arthur Ellis, 6 Jonathan Thomas, 5 Sam Williams, 4 Lloyd Peers, 3 Campbell Johnstone, 2 Scott Baldwin, 1 Marc Thomas.
Replacements: 16 Matthew Dwyer, 17 Duncan Jones, 18 Dmitri Arhip, 19 Ian Gough, 20 George Stowers, 21 Dan Baker, 22 Tom Habberfield, 23 Kah Fotuali'i.
Harlequins: 15 Ross Chisholm, 14 Seb Stegmann, 13 Matt Hopper, 12 Ben Botica, 11 Sam Smith, 10 Rory Clegg, 9 Karl Dickson, 8 Tom Guest, 7 Luke Wallace (c), 6 Joe Trayfoot, 5 Charlie Matthews, 4 Sam Tworney, 3 Will Collier, 2 Dave Ward, 1 Mark Lambert.
Replacements: 16 Henry Allen, 17 Darryl Marfo, 18 James Johnston, 19 Charlie Walker, 20 Maurie Fa'asavalu, 21 Jordan Burns, 22 Louis Grimoldby, 23 Ollie Lindsay-Hague.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.