Liverpool manager Jurgen Klopp said his side could only blame themselves after the last year's Champions League runners-up were overrun by Napoli before Lorenzo Insigne's late victor gave the Italians a 1-0 win to go top of Group C on Wednesday (Oct 4).
"Yes, it is a tough game [v City]", Klopp said.
Klopp accepts a draw would have been more than they deserved and feels the formation Liverpool used was a mistake.
"We were not good enough and if you are not good enough, you'll lose and that happened to us tonight".
He said: "I heard it's a back problem, but we don't know exactly - we have to wait".
"We defended with 4-4-2, the same as many other times".
"Now, let's have a look afterwards, how the players are, what happened in the game, injury-wise, little knocks and stuff like that".
The German was left frustrated by his attacking trio of Mo Salah, Roberto Firmino and Sadio Mane as the Reds failed to register a single shot on target in the competition for the first time in 12 years.
The Reds reached half time without registering a shot on target for only the second time this calendar year, but there was a bit of work for Alisson Becker to do when he collected an Arkadiusz Milik effort on the turn at the second attempt. We had to fight really hard. That's what we're going to do - we're going to analyse the game and see what we can do better.
Liverpool lost Naby Keita to injury midway through the first half with the £53m summer arrival departing on a medical cart and taken for further examination. "We have to take it as a lesson and then we have to carry on".
Liverpool now turn their attention towards Sunday's encounter with Manchester City at Anfield as they look to maintain their unbeaten start to the league campaign. You were all full praise of our season and then tonight we didn't perform. Then we will prepare for Sunday.