This is per an appearance on the podcast The Town With Matthew Belloni (via Consequence), where Jaysen recalled an instance of Dylan meeting with director James Mangold for a table read of the script.

Guess if you want a thing done well, you got to do it yourself. Bob Dylan Tested A Complete Unknown Script by Performing as Bob Dylan

A Complete Unknown' follows Bob Dylan's life in the early 1960s as he begins his career, culminating in a performance at the 1965 Newport Folk Festival. Here's a look at the music icon's life nearly six decades after 'A Complete Unknown' leaves off.