Ryan is able to include five returning internationals - hooker Andy Titterrell, number eight Gareth Delve, full-back Iain Balshaw, scrum-half Gareth Cooper and winger James Simpson-Daniel.
Titterrell returns after the shoulder problem he picked up against Newcastle before Christmas and comes in for Olivier Azam, who moves to the bench.
Delve returns to the number eight position following a knee injury, Balshaw has recovered from a gashed knee to replace Willie Walker at full-back and Cooper comes at scrum-half for Rory Lawson. Simpson-Daniel has recovered from flu.
"We are fortunate to have some key players returning to the squad," Ryan said. "Tomorrow represents what the Heineken Cup means across Europe - there are some huge contests and ours falls right into the top bracket.
"This is the top end of club competition and we will relish that fact. We have made a very encouraging start in the Heineken Cup but we know tomorrow will examine us and what we can offer this tournament.
"These are the sort of games you want to be involved in as a player and a coach and that is what makes it such an exciting prospect."
Gloucester have taken 19 points out of a possible 20 in the Heineken Cup so far this season and a victory tomorrow will guarantee them a place in the knockout stages.
Lesley Vainikolo was not considered for selection following the death of his father in New Zealand.
Either side of Titterrell will be props Nick Wood and Carlos Nieto; Marco Bortolami will skipper the side from the second row alongside Alex Brown.
Peter Buxton, Akapusi Qera and Delve complete the back row.
Cooper returns following a hamstring strain to partner Ryan Lamb at half-back, while Mike Tindall and Anthony Allen are the centre partnership.
Balshaw, Simpson-Daniel and Leon Lloyd complete Ryan's back three.
"We have a strong squad and we are comfortable with the selections we have made for this specific game," Ryan added. "It gives us dynamism with the option of power from the bench. Bar one or two exceptions, we have everybody available this weekend."
On the bench, Azam is joined by prop Christian Califano. Luke Narraway and Alasdair Strokosch complete the forward options, while Rory Lawson, Chris Paterson and Walker are the three-quarter options.
GLOUCESTER (V Ospreys, tomorrow, 5.30pm): Iain Balshaw; James Simpson-Daniel, Mike Tindall, Anthony Allen, Leon Lloyd; Ryan Lamb, Gareth Cooper; Nick Wood, Andy Titterrell, Carlos Nieto, Marco Bortolami (capt), Alex Brown, Peter Buxton, Akapusi Qera, Gareth Delve. Reps: Olivier Azam, Christian Califano, Luke Narraway, Alasdair Strokosch, Rory Lawson, Chris Paterson, Willie Walker.
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