There could be a feature film based on League of Denial coming in the future after Parkes/MacDonald Productions partners Walter Parkes and Laurie MacDonald won the rights to the book in an auction.
Does this means that there *will* be a film coming? Of course not. There's no script, no story, and no casting, but if a film does arise, it will be coming from this production company, known for the Men in Black franchise, Gladiator, and Flight, among other films.
There are plenty of stories that could be told from the book, including a realistic, more fleshed-out version of the critically acclaimed Frontline documentary. But more than likely, if a film is made, it will focus on the struggles of Mike Webster after his NFL career because that's the most well-known story that came out of the book.
But again – if a film is made, on either the big or the small screen, it won't pop up until much further down the road. If Parkes and MacDonald do come up with an interesting story for a film based on the book, they really need to be careful to not trivialize the seriousness of CTE and turn the real-life struggles of these players into a Hollywood drama.