Manchester City manager Roberto Mancini has warned Mario Balotelli he must improve after the striker's poor display against Manchester United.
Balotelli was preferred to Carlos Tevez but replaced by the Argentine early in the second half as City lost 3-2 to their title rivals.
Mancini said: "I love Mario as a guy and a player but it is important for him to start to think about his job.
"He has everything to play well but he can't continue to play like today."
Balotelli was out of favour and then injured for much of November before being restored to Mancini's starting XI and scoring his only Premier League goal of the current campaign in City's vital victory at Wigan.
He returned to the bench for last weekend's 1-1 home draw against Everton, but was restored for the visit of United in Sunday's showdown between the top two.
However, the Italy international failed to impress Mancini and was withdrawn in the 52nd-minute as City trailed 2-0 to their neighbours.
Tevez's introduction re-energised City and goals from Yaya Toure and Pablo Zabaleta restored parity before Robin van Persie fired in an injury-time winner for United.
Mancini added: "We want more from Mario because he has everything. He has top quality.
"When you have a player of this quality you can't understand that he could continue to throw this out of the window. This is incredible.
"I saw a player like this in my life with fantastic quality but in the end they did nothing. I don't want Mario to finish like this player because it's not good for him.
"I wanted to see if Mario did well at the start of the second half but after the five minutes he played I saw that he was playing like in the first half."
However, Mancini defended his decision to start Balotelli, who walked straight down the tunnel following his substitution before later returning to the dugout, ahead of City's leading Premier League scorer Tevez.
He said: "It is easy to say after the game. I thought Mario could create problems for them. He is young and runs quickly - when you decide before the game this is what you think."
City's manager still believes they can retain their title, despite now trailing United by six points.
He said: "We showed fantastic spirit. We are still strong and I am sure we can win the double this year."