Steffen is set to start against Marseille at the Etihad Stadium on Wednesday as Pep Guardiola looks to rotate his squad with qualification from Group C already secured. Steffen has made two appearances in the Carabao Cup so far this season and is likely to get the nod to step in for usual No. 1 Ederson.
"[I've been] watching the Champions League for as long as I can remember," Steffen said on Tuesday. "Walking out and hearing the song is going to be really special for me and my family. I am excited to get out there and play another game, looking forward to that."
Steffen has spent much of this season on the bench as back-up to Ederson after arriving from a period on loan at Fortuna Dusseldorf in the summer.
But the 25-year-old, capped 19 times by United States, insists he is not worried by a lack of game-time affecting his performance against Marseille.
"The goalkeeping staff do a really good job of continuing to push all the keepers on a day to day basis," he said. "They are really detailed. You can't really just come into training and give 50 percent, you have to give 100% every day. That is why we are one of the best clubs in the world."
Steffen has been a vocal supporter of the Black Lives Matter movement that has seen players across England take the knee before every game.
The gesture was booed by a section of Millwall supporters on Saturday and the Pennsylvania native says it evidence that more education is needed on the issue of racial equality.
"It is very disappointing but it also opens up your eyes again. Obviously not everyone fully understands the situation -- that is OK," Steffen added.
"We can't teach everyone but we can at least talk to people and have these discussions and try and show them why we are fighting, why we are taking a knee, why we are trying to give back to the disadvantaged communities who have been oppressed."