Fox played iconic teenage hero Marty McFly in three films, and previously admitted he would be happy to see the movies rebooted with a new, young cast.
He said, "I'm 44-years-old now and I'm not interested in running around on skateboards!... I think if they did it again now they would do it with a younger cast and just do a different realisation of it, which would be fun."
But director Robert Zemeckis and screenwriter Bob Gale are adamant they would never move forward on the project without Fox, who was diagnosed with Parkinson's disease in 1991 and semi-retired from acting in 2000 when his symptoms worsened.
Gale tells ComingSoon.net, "The story is closed. When Michael J. Fox was diagnosed with Parkinson's we said 'Come on. Who wants to see a Back to the Future movie if Michael J. Fox isn't in it?' I don't. He didn't. Nobody does."
Zemeckis adds, "I think three is a good number to end on. Three is enough."