City's latest loss came at the hands of Villa, who ran out 2-1 winners over the current champions to hand them a ninth loss from their last 12 matches in all competitions.
City have already lost twice as many league games this term as they did throughout the whole of last season on their way to winning a fourth successive title.
Lewis, the 20-year-old England international, admitted it is a "difficult" time at City right now.
"There's leaders in the dressing room that are natural leaders. They can speak, everyone listens and everyone agrees.
"But when it comes down to it, it's not what is said in the changing room, it's what we're doing on the pitch. That's what needs to be solved.
"Nobody is going onto the pitch saying, 'I'm not doing that', or 'I don't want to win'. It's difficult right now but we have to stick together.
"There's different things to put your finger on but it's just not right at the moment."
City's problems at the back are continuing to grow - they have only managed one clean sheet in their last 10 in all competitions.
Conceding twice on Saturday took their season tally to 25, only nine short of their total throughout the entire 2023-24 Premier League campaign.
Lewis added: "Everyone in world football concedes a goal but because we hold ourselves to such high standards, when we concede we're so disappointed in ourselves, that's when you'll see more mistakes come.
"At the start of the season we conceded a few goals first but we just bounced back straight away. That can be down to confidence, many things, tired legs. But we need to get back to the way we want to be."
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