James Corden will play the winner of the first series of Britain's Got Talent, with The Devil Wears Prada director Frankel at the helm.
Frankel today (August 31) revealed to Digital Spy that, while deals are still yet to be finalised, the film's major roles have all been cast.
The Iron Lady's Alexandra Roach will play Potts's girlfriend and later wife Julie-Ann Cooper, alongside Mackenzie Crook as his best friend, and Julie Walters and Colm Meaney as his parents.
"We start shooting in about six or seven weeks," Frankel said. "It'll be done by Christmas."
"It's just the Rocky story. I think most people were not aware of the full extent of the adversity that [Potts suffered], but it's also a love story.
"It's a story of this guy who meets a woman online, a guy with no confidence, still living at home with his parents and working in a Carphone Warehouse, and he meets this woman who just believes in him.
"Almost for no reason. Because she loves him, she believes in him, and she won't let him give up his dream."
It was previously reported that Katy Perry had been approached to play the role of Julie-Ann.
Frankel's next film Hope Springs, starring Meryl Streep and Tommy Lee Jones, comes out on September 14 in the UK.
Watch an exclusive featurette featuring Streep and Jones below: