Martin Petrov says Manchester City have "no chance" of winning Sunday's derby at Old Trafford unless they buck their ideas up.
"The class of both teams became visible in the game against Arsenal. They showed that they are the better side and beat us deservedly with better play," he said.
"If we approach the derby against Manchester United in the same way we will have no chance.
"We must play with much more ambition and much harder as this game will be even tougher than the one versus Arsenal. I think it will be great for our fans if we manage to do something against United at their stadium.
"We must be very disciplined tactically on the pitch because these teams win mainly due to their tactical discipline and of course the quality of their players.”
The 29-year-old said he would be even more focused than usual when he steps out against the reigning champions.
"Everybody can see how strong Manchester United and Arsenal are as they occupy the top two places in the Premiership standings. The motivation when you play against these teams is always at the highest level."