Milan are selling Balotelli to Liverpool today.
Trapattoni said: "When the right train goes by, you have to get on it. It can happen once, twice, three times. Not a thousand.
"Suddenly you can find yourself old and forgotten. Mario is riding an uncontrollable powerboat, he mustn't waste this moment of his life.
"Above all, his agent Mino Raiola must not see him only as a goldmine to be taken advantage of, but help him understand his mistakes.
"Milan have some talented players. I bet this season we'll see the explosion of Stephan El Shaarawy on the scene."
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