The Goodfellas filmmaker is hoping to bring the Rat Pack star's life story to the big screen but Scorsese reveals he's struggling to come up with a focused script, although he hasn't ruled out developing a Sinatra TV miniseries.
He tells ETOnline.com, "I'm talking to one or two writers now. The problem is the biography. Where do you start? ...I met this writer who I think could do a lot with it, but (we) have to get a hold of the story. It's too unwieldy. I'd love to tell the whole story, but the idea of art is to figure out where to start because we can't tell his whole life story. If we told the whole story of Sinatra, it would be 15 hours...
"I love the idea of a miniseries - particularly working with HBO (TV network) because, as long as you stay reasonably on budget, you have freedom, which is very difficult to find in the cinematic marketplace."
And while his longtime pal Leonardo DiCaprio, who Scorsese directed in both The Departed and Shutter Island, has expressed an interest in taking on the lead role, the Oscar-winning director is keeping his options open.
He adds, "Leo's always talked about doing it, but what if the story takes you in a completely different way? We could go for an unknown. Maybe the person who plays him isn't important. Maybe it's distracting to have a star in that role."
But one thing's for sure - Scorsese's choice for Sinatra won't be singing in the project: "You can't have someone else sing! It's got to be Sinatra's voice. It's tricky."
Sinatra died of a heart attack in 1998, aged 82.