Manchester City ace David Silva has warned his team-mates to be wary of reawakening the "beast" of Real Madrid.
The Premier League champions kick off their Champions League campaign with a trip the Bernabeu to take on out-of-sorts Real.
Real have endured a difficult start to their Primera Liga defence, winning just one of their opening four games and already lie eight points behind arch rivals Barcelona.
Silva, who signed a new long-term deal at City on Monday, fears a big European night could provide the spark for Real to recapture their top form.
"It is clear that, when everything is going well, they play with more confidence," said Silva. "When they have doubts, it is difficult.
"But maybe it is more dangerous because they are not at a good moment and we could awaken the beast in them. We have to be careful - they are a world-class team."