The actor, who previously worked with Scorsese on Howard Hughes biopic The Aviator and other movies, is said to be training with a voice expert to learn how to mimic the late Rat Pack crooner's distinctive sound.
A source tells British newspaper The Sun, "Leo has hired a top vocal coach to get him sounding like Sinatra. He is a massive fan of the singer and has always wanted to play him. He would be sick to miss out on the leading role because his singing wasn't up to scratch. He is now in intensive vocal coaching lessons to replicate Sinatra's distinctive style."
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