Garcia's men were thrashed 7-1 at home in Group E against Bayern last month and the teams meet again on Wednesday with the Frenchman not confident of springing a surprise in Munich.
"We have a small chance of coming away with a positive result, perhaps one in 10," he told a media conference on Tuesday.
"What matters is our performance.
"The last match against Bayern was a blip.
"We hope to upset the odds but the main thing is that we put in a gutsy display, that we're aggressive and compact.
"If we do get our heads down and give them a fight we can do well. We want to enjoy this campaign.
"We're not going out there feeling sorry for ourselves. We'll see if we give a better account of ourselves than last time.
"Whatever happens won't determine anything regarding qualification, we'll still have two games to play."
Midfielder Miralem Pjanic insists the heavy defeat at the Stadio Olimpico provided a steep learning curve for Roma.
"We played badly in the first game but we learned a lot from that defeat," said the 24-year-old.
"[Wednesday's match is] a rematch but it won't be a repeat of what happened in Rome. We want to prove the difference isn't so great.
"We're confident in our ability and we're set on showing that tomorrow against one of the best teams in Europe."
