However, the Guinness Premiership leaders are the only team in the Heineken Cup to boast a 100% winning record. Gloucester took the points in a tight 26-18 encounter at Kingsholm in November and this should be another tough contest.
Shane Williams returns after a knee injury looking to keep the Welsh region's hopes of a Heineken Cup quarter-final spot alive at the Liberty Stadium.
Williams, 30, said: "Tomorrow's game is arguably the biggest in our history; with so much at stake and possibly a full-house so it doesn't get any bigger or better than this.
"There will be a fantastic atmosphere and we can't wait. We're all hoping this is the match where the Ospreys come of age in terms of European rugby.
"The Heineken Cup is the Holy Grail of northern hemisphere rugby. Every professional player wants to win it and I'm sure our supporters will be sharing our excitement ahead of such a huge occasion."
The Ospreys recall several of their big guns with Wales international centre pair Gavin Henson and Sonny Parker back in coach Lyn Jones's strongest possible starting line-up. British Lion Henson, 25, has been sidelined since breaking a bone in his hand in the EDF Energy Cup at Harlequins six weeks ago while Parker makes his comeback after knee surgery.
Gloucester have named Wales's Gareth Cooper at scrum half while No.8 Gareth Delve will be looking to impress new Wales Coach Warren Gatland who names his Six Nations squad on Monday.
Ospreys: L Byrne; N Walker, S Parker, G Henson, S Williams; J Hook, J Marshall; D Jones, H Bennett, A Jones, I Gough, AW Jones, R Jones (Capt), F Tiatia, M Holah
Replacements: R Hibbard, P James, I Evans, J Thomas, M Phillips, M Taylor, J Vaughton
Gloucester: I Balshaw; J Simpson-Daniel, M Tindall, A Allen, L Lloyd; R Lamb, G Cooper; N Wood, A Titterrell, C Nieto, M Bortolami (Capt), A Brown, P Buxton, G Delve, A Qera
Replacements: O Azam, C Califano, L Narraway, A Strokosch, R Lawson, C Paterson, W Walker