Forward Abel Ruiz became the latest to join Girona's long injury list which includes Viktor Tsygankov, Oriol Romeu, Jhon Solis, Portu, Bryan Gil, Pau Lopez and Yaser Asprilla.
Girona now have only 12 outfield players from the first team to play at Montilivi stadium on Tuesday since midfielder Gabriel Misehouy has been registered with their B team.
"We have no one back and we are missing Abel Ruiz due to adductor problems. Misehouy is also missing because he can't play," Michel told reporters.
"Marc Aznar, (Juan) Arango, Selvi (Clua), and two goalkeepers will come from the reserve team and we have to evaluate them. Even so, we have 11 players to form a starting side."
Girona, who had never qualified for European competition in their 94-year history, secured a place in the Champions League by finishing third in LaLiga last season but are so far winless on the continent.
Michel said his side must value their place in the competition.
"Playing Champions League with Girona cannot be just another game. I don't want to tiptoe around this competition and that people don't give it the value it has," the coach said.
"It has a lot of merit for what we have done and also for the club, which has made efforts, and we have to enjoy it and value it. For me, tomorrow is a very special day, just like the two previous matches."
Girona lost to Paris St Germain last month following a 90th-minute own-goal and then slipped to 3-2 defeat at home by Feyenoord.
"To have a chance of advancing to the next round, we need to win... the standings tell us that we must get the three points," Michel added.