Manchester City defender Pablo Zabaleta fears Chelsea could be at their most dangerous this weekend.
The Argentinian believes the appointment of Rafael Benitez as interim manager after a week of turmoil at Stamford Bridge could spark the Londoners back into life.
That is something the champions and Barclays Premier League leaders are wary of ahead of their trip to west London on Sunday.
Zabaleta said: "It's a difficult moment for them but they now have a new manager in Rafa Benitez.
"When they are in a moment like this, it might seem they are easier to play against, but a new manager can make old players fresh again.
"Benitez has experience in the Premier League so it will be a really tough game for us."
Chelsea began the month as Premier League leaders but have slipped to third after a run of four games without a win.
"A new manager can make old players fresh again" - Pablo Zabaleta
That sequence piled the pressure on manager Roberto Di Matteo and he was then axed by the club after defeat to Juventus on Tuesday seriously damaged their Champions League prospects.
City's own hopes of progressing in the elite European competition were ended on Wednesday as they drew 1-1 with Real Madrid at the Etihad Stadium.
Roberto Mancini's men had needed to win to stand any chance of avoiding premature elimination for a second successive season.
They will hope to put the disappointment behind them as they turn their attention back to their title defence, in which they remain unbeaten and well on course.
City moved to the top of the league for the first time this season with a 5-0 demolition of Aston Villa last weekend.
Zabaleta, 27, said: "Once you finish a Champions League game you have to refocus your mind, and we have to now look at Chelsea.
"We need to keep working hard for our unbeaten record" - Pablo Zabaleta
"It's a different situation in the Premier League - we are top and play the team that is third, so it is an important game for us."
City were unbeaten in the Premier League last season until playing at Chelsea in December.
Zabaleta said: "We need to keep working hard for our unbeaten record - if we can get three points at Stamford Bridge it would be great for us."
City knew their European chances were slim but striker Sergio Aguero said earlier in the week he remained confident of repeat Premier League success.
Aguero said in City's programme for the Real match: "I'm sure we will retain our title.
"It's true Chelsea, (Manchester) United, Arsenal and the other teams have strengthened their squads intelligently - we are the champions and they want to take us on.
"But it won't be easy for them because we are growing as a team and we know each other better every time we play.
"We are destined to win more trophies and barring any major setbacks, we will."
City were awaiting an update on the fitness of captain Vincent Kompany, who suffered a knee injury against the Spanish giants.