Ramos was sent off in the first leg as Los Blancos lost 2-1 to Pep Guardiola's side at the Santiago Bernabeu prior to lockdown and the Madrid captain misses the second leg of the last-16 tie through suspension.
"Sergio is such an important player for us," Varane said in Thursday's pre-match press conference.
"But we are a group and everyone has their role. I'm a player who likes to cover for the rest. I talk to my team-mates a lot in the dressing room on a tactical level.
"We know Sergio's importance in the group as a whole and we will have to play a great game to qualify."
Ramos has been included in the 24-man travelling squad and will allowed in the dressing room with his team-mates at the Etihad Stadium.
"Tomorrow it's clear we have to score and we have to attack," Varane added. "Our goals can come from many players, who have different and complementary qualities.
"The changes can also prove decisive in these games. We have a squad that can make the difference in matches like these."