The beloved, 63-year-old action star sparked concern over the summer when he was photographed looking uncharacteristically frail.
"Martin wanted us all to look a bit more gaunt, which [co-stars Adam Driver and Andrew Garfield] did as well," Collider.com quoted Neeson as saying at the 4th annual Los Cabos International Film Festival.
"I know Adam went to the extreme. He's an ex-marine and when he's given an order, he follows it through. He was like something out of Auschwitz. Martin requires this level of [dedication] and I think it pays off."
Neeson and Scorsese previously collaborated on 2002's Gangs of New York.