Manager Pep Guardiola made nine changes in preparation for the first Manchester derby of the season but still closed out Group C with a fifth win from six games to finish with a club-record 16 points.
Ilkay Gundogan was substituted at half-time because of a minor ankle injury while Guardiola revealed Aguero will not start against Manchester United despite marking his return from injury with a goal.
“His instinct to score will always be there,” said Guardiola about Aguero. “He had three or four training sessions and the reaction was good. He had 25 minutes and scored a goal so step by step.”
It was Steffen’s third start for City after returning from a loan spell in Germany with Fortuna Dusseldorf having playing in two Carabao Cup ties earlier in the season.
“I love shut-outs! The guys in front of me did a really good job in terms of limiting their chances and I didn’t really have too much to do so kudos to the guys in front of me,” Steffen told the club’s website.
“We wanted to get the win and a shut-out to keep the confidence going ahead of the derby at the weekend.”
“It’s a big game and we’re excited for it.”
The 25-year-old, who made two saves, is one of a record 10 USMNT players who were named to Champions League squads for this season’s competition alongside Christian Pulisic [Chelsea], Giovanni Reyna [Borussia Dortmund], Tyler Adams [RB Leipzig], Weston McKennie [Juventus], Sergino Dest [Barcelona], Konrad de la Fuente [Barcelona], Chris Richards [Bayern Munich], Ethan Horvath [Club Brugge] and Alex Mendez [Ajax Amsterdam], with nine making at least one appearance in the group stages.