It was a marker that they were coming for Chelsea's title.
Klopp was asked if the Liverpool midfielder would be fit for the City clash in his pre-match press conference, and admitted he was unsure.
Manchester City fullback Kyle Walker insists Liverpool fans can forget about trying to intimidate them at today's showdown. At the time of doing this column I can't offer an explanation beyond: we weren't good enough.
Guardiola's Manchester City side won the Premier League title last season with a record points tally of 100 - however, the Spaniard was full of praise for the impact Klopp has had at Anfield recently.
Defender Walker added: "We're the champions and we have a point to prove". But last season we proved on a couple of occasions we are more than capable of going blow-to-blow with them and producing performances that deservedly win games against them.More news: Lewis Hamilton clinches Russian Grand Prix
The Belgian was expected to be out for three months but returned to training earlier this week. For what? We arrive there, both sides, to play a Premier League game.
Liverpool have drawn most of the plaudits for their start to the campaign but go into the match on a three-match winless run, with defeat and then a draw against Chelsea in cup and league before the 1-0 Champions League loss in Naples. Sterling has started the season superbly and has four goals and two assists in six Premier League games, the 23-year-old is playing some of the best football of his career and don't be surprised if he scored against his former club. Liverpool's defence has performed well this season, although space can open up in their right-back zone - Eden Hazard twice got in behind in that zone last week. When somebody's telling me, "Good luck for Sunday", I think always, "Unfortunately, we need it".
"We respect Manchester City for what they've achieved and the quality they have, but it's respect and not fear".
Napoli's pressing didn't allow the front three any time on the ball and they should expect much of the same against City, so they'll have to get rid of the ball much quicker and play more of those little passing triangles they manage to pull off so well.
City's team bus was attacked outside the stadium when it last visited the ground for a Champions League tie in April, with windows smashed as it was hit by missiles.