Pep Guardiola believes relegation-threatened Swansea are now a formidable proposition under Paul Clement.
Swansea have climbed out of the Premier League's bottom three with three wins from four games since former Real Madrid and Bayern Munich assistant manager Clement took charge last month.
One of the those victories came away against title-chasing Liverpool, and Manchester City boss Guardiola is expecting a difficult afternoon as the Swans visit the Etihad Stadium on Sunday.
He said: "I am really impressed. I saw their game against Liverpool and I have started to watch the game against Southampton.
"I tried to discover the way to attack them and - wow - I couldn't find it. It's so complicated.
"When I see their games I can see his hands on it. They are so well organised.
"There is no space in the middle. When you go and attack outside they defend really well in the box. Then they have long balls to the striker with (Fernando) Llorente. They have quality players for the counter-attack.
"It will be a really tough game, one of the toughest until the end of the season.
"Now they are in a good moment, won three of the last four but is also the way they play. They won at Anfield and beat Southampton, big teams. It will be really tough but hopefully we can win two in a row."
City have started to show signs of getting back to their best after an inconsistent spell. Since losing 4-0 at Everton last month City have been impressive in a 2-2 draw with Tottenham and won convincingly at Crystal Palace - in the FA Cup - and West Ham.
Their attack has looked potent with the speedy forward trio of Gabriel Jesus, Raheem Sterling and Leroy Sane particularly catching the eye.
Guardiola has been pleased with the forwards but also recognises the defence has tightened up.
He said: "The last two games we have made a clean sheet. I think it's easier to solve the problems in our box than the opponents'.
"The most difficult thing in football is to score a goal. That's why the guys who score the goals are the most valued players in terms of salaries for example or the reputation in the media.
"I think it's easier to concede few and this is so important for our stability."
Guardiola is still to decide who will play in goal having preferred Willy Caballero to usual first choice Claudio Bravo for the past two games.
He said: "I felt that Willy should play. Of course confidence is important but I still have the same confidence in Willy and Bravo. I'll choose depending on how I see them."
Source: PA
