Roberto Mancini insists Mario Balotelli must lighten up to justify his new status as the world's best youngster.After winning the Fifa award, Balotelli claimed not to have heard of Arsenal's runner-up Jack Wilshere while saying he is nearly as good as Lionel Messi. [LNB]But City boss Mancini says he must back up his words with consistent displays - and curb the temper blighting his game. [LNB]"Only if you play well in every match can you say these things," he said. "You need to smile to play football." [LNB]Balotelli has shown flashes of brilliance since his £24 summer arrival at Eastlands from Inter Milan, but he has also been sent off while enhancing his reputation as a headstrong maverick. [LNB]Mancini expects the 20-year-old to be fit for the Boxing Day trip to Newcastle after his ineffective performance in Monday's 2-1 home defeat to Everton, when he was eventually substituted because of injury.[LNB] Will Balotelli prove his worth? But, if he is involved at St James' Park, former Inter Milan manager Mancini would like to see a lighter approach than the one he has witnessed recently - and a more effective performance. [LNB]"If he thinks what he says [that he can make as big an impact on football as Barcelona's world player of the year Lionel Messi] he must show it in every game," he said. [LNB]"The Premier League is so different from the Italian league. Mario must understand. [LNB]"He must improve in this situation. [LNB]"You need to smile to play football. That's the best thing you can do. [LNB]"It is good when a player has confidence in himself. Mario Balotelli has everything you need to be one of the best players in the world. But he must improve and he must show it. It depends on him."