The Back to the Future star, 59, was diagnosed with the long-term degenerative disorder of the central nervous system in 1991.
Since then, he has continued to act with roles in Spin City, The Good Wife and Curb Your Enthusiasm.
But, in a new interview, Fox said that “acting is getting tougher to do” as it has affected his short term memory so much he can no longer remember his lines.
"I’m down to this," Fox told People. "My guitar playing is no good. My sketching is no good anymore, my dancing never was good, and acting is getting tougher to do.
The actor suggested he will write instead, stating: "So it’s down to writing. Luckily, I really enjoy it.”
He added that he "always had a real proficiency for lines and memorisation", but said he "struggled" with recent word-heavy roles.
Fox played Marty McFly in the Back to the Future trilogy from 1985 to 1990.
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