Pep Guardiola can't afford to rest on his laurels at Manchester City.
The Catalan may have established his reputation as one of the best managers in the game long ago, but he is well aware that he has plenty of work to do at the Etihad.
A 2-1 win over Manchester United put his side top of the Premier League table, but Guardiola still had a warning for his players about their current form.
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"Until now in the Premier League it has been okay, but to compete against the best clubs in Europe, in this moment with the way we are playing, we are not able to," he told Sky Sports.
"If you ask me whether we are ready to compete in Europe, we are not ready. We create, but in front we need more. But it is just two months together, so we have time to get better."
It's no surprise that City weren't quite at their best in attack, with main man Sergio Aguero sitting out suspended for violent conduct in the West Ham game.
In his absence, it fell to Kevin de Bruyne to run the show, and it has to be said that he'd surely compete against any team in Europe right now.
But Guardiola knows all too well what it's like to fail in the Champions League. Although he won the competition twice with Barcelona, it was the one blot on his copybook at Bayern Munich.
City's big problem
City have been drawn in a mixed group with Barca, Celtic, and Borussia Monchengladbach, but the manager has identified one key area they need to work on if they're going to seriously compete this season.
"We have had a little bit of a problem in the last few games with the last pass.
"There was the chance to make counter attacks, and we had many. But, except for one or two from Kevin De Bruyne, we didn't finish."
Last season, Manuel Pellegrini's outfit reached the semi-finals before losing to eventual winners Real Madrid, and it is the one trophy that continues to elude them.
Where do City rank among Europe's top sides? Will they be a force in the Champions League? Have your say in the comments.