His presence on set has been “essential,” the “Indiana Jones” actor told Variety in an interview published Wednesday, saying that Fox “gives me both a physical representation of the disease to inform myself with, but more than that, he allows me to believe that Paul could believe that he could be adequate to the challenge.”

Fox came out of retirement to star in the series, which features Ford as a therapist who has Parkinson's disease

In 'Shrinking', Ford portrays the quirky but warm-hearted Dr. Paul Rhoades, an aging psychotherapy icon who has been diagnosed with Parkinson's. Fox, who received the devastating diagnosis in reality at just 29 years old in 1991, plays a yet-to-be-revealed role in the third season of the series.