The Guinness Premiership play-off contenders cannot secure quarter-final status from Pool Two, while Kingsholm visitors Leinster need a bonus point victory to guarantee a home draw after clinching top spot one week inside the distance.
Ryan will be without the services of injured trio James Simpson-Daniel, Anthony Allen and Olly Morgan - all three players suffered knocks during last Friday's defeat in Agen - but he still a parades a line-up containing eight internationals.
Ryan said: "In a game of last week's intensity there are obviously some casualties, and we are not in a position to risk anyone at this stage.
"We have been involved in some extremely physical contests at the top end of Europe and the Guinness Premiership since the turn of the year, and these things happen.
"Nevertheless, we have a strong squad for what is an important game for us. Leinster have already won the pool, but we want to test ourselves against that calibre of opposition.
"Europe has been a lost opportunity for us this season, yet there is still plenty on the game tomorrow. There will be a capacity Kingsholm crowd, and we are fully motivated."
Leinster welcome back Brian O'Driscoll and Girvan Dempsey for their west country mission, knowing a bonus point triumph would guarantee a top four seeding, as neither Pool One leaders Wasps nor Pool Three front-runners Stade Francais could then catch them.
"We know that our chances of progressing further will increase if we get a home quarter-final," said Leinster coach Michael Cheika.
"We are very motivated to manage our destiny, and we know that we have to peak on Friday night."