The Italians can claim victory in what has been a tight three-way battle for the runners-up spot in Group E with City and CSKA Moscow by beating the English champions at the Stadio Olimpico.
But it is certain to be a night of high tension with all three teams going into the crunch final round of fixtures locked on five points and with little margin for error.
Anything less than victory would open for the door for CSKA or City to nip in and join Bayern Munich in the last 16.
Garcia said: “We need to make the most of every moment. We’re looking to pull it off, a win would be incredible.
“We know that City are a good side and it will be very tough tomorrow but I’m sure we can do it. Every match is important but tomorrow’s is special because it’s like a cup final.
“We should have been out of the running by this stage because we were in the fourth (seedings) pot and yet we’re still in the hunt.
“The fact that we are still in the race means that we have quality. Credit to us that we still have the chance to play this cup final in front of our fans at a passionate Olimpico.”
The permutations for the group are complicated. Roma could still go through with a goalless draw, but only if CSKA do not beat Bayern. If CSKA draw, any draw would suffice for Italians. But if the Russians lose, only a goalless draw would be adequate because, in that scenario, a score draw would mean City going through.
Garcia does not want to get bogged down in the complexities of it and will just be focusing on obtaining victory, regardless of events in Munich.
The Frenchman said at his pre-match press conference: “There is no choice, we just have to play to win and not for other things. We can only decide our own fate with a win. We can’t know what happens in the game between Bayern and CSKA.
“The Germans did not win the fifth game and could do the same with the sixth. For us the only possible scenario is to score and win the match.”
Garcia has no concerns about the state of mind of midfielder Daniele de Rossi.
De Rossi was sent off in Saturday’s draw against Sassuolo, days after reports emerged claiming his ex-wife Tamara Pisnoli – to whom he was married from 2006-09 – had been arrested as part of an investigation into an alleged kidnapping scandal.
Garcia said: “Daniele is fine. We won’t have him for the Genoa game, but he’s a very important player, a great champion and a crucial figure in the dressing room.
“He’s played over 100 times for Italy, he’s a champion both on the field and in life.”