Martin Scorsese has teased that an unknown actor may take the lead in his upcoming Frank Sinatra biopic.

Leonardo DiCaprio had been tipped to play the late musical legend in the drama, but the Oscar-winning director has now hinted that may not be the case.

"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," said, Belfast Telegraph reported citing Entertainment Tonight.

"Maybe the person who plays him isn't important. Maybe it's distracting to have a star in that role. Yet, you can't have someone else sing!"

The filmmaker added: "It's got to be Sinatra's voice. It's tricky. It's filled with problems - and whatever you do, there's always going to be people who don't like it, so you have to find something special. And I think I've found it. Now's the time to execute it on the page."

Martin - who will work again with Leo this summer for the financial drama The Wolf Of Wall Street - revealed he's still deciding which era to focus on for the music star.

"I'm talking to one or two writers now. The problem is the biography. Where do you start?" he continued.

"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," he added.