Khan began working with Roach after a devastating loss to Breidis Prescott in 2008. In the same stable as pound-for-pound king Manny Pacquiao, the Bolton-born fighter began to fight regularly out of the US, rehabilitated his career, and became a world champion under Roach.
He said of Roach: "It’s hard to see him older and getting worse. Freddie, with the Parkinson’s disease, he was struggling with instructions and couldn’t move as well."
Roach, who has been named trainer of the year for three of the last four years, hit back at Khan's comments, saying that his camp had asked him to concentrate on Khan solely before then leaving his stable.
"If that was true (that my Parkinson's was an issue), why would he say to me fire Manny Pacquiao and (Julio) Chavez Junior and they would keep me?” said Roach in response to Khan's comments.
"Him, his father, his lawyer and his uncle all said that. It had nothing to do with Parkinson’s. Parkinson’s had nothing to do with it. They know that. And I wish them the best of luck."
After being criticised for bringing up the Parkinson's, Khan looked to backtrack and clarify his relationship with Roach on Twitter.
"Hey guys I didn’t say @FreddieRoach is a bad trainer, he’s 1 of the best out there and took my career to a high winning 2 world titles,” Khan wrote.
"I blame myself for the losses in my career. Not blaming @FreddieRoach or anyone. I just needed a change.”
The 25-year-old will make his first appearance under the tutelage of his new coach – Virgil Hunter – against Carlos Molina in Los Angeles on December 15th.
Hunter was voted trainer of the year in 2011 after helping Andre Ward to win the Super Middleweight 'Super Six' championship with a dominant points victory over Britain's Carl Froch.