Lee Child, who pumps out the Reacher books yearly, insists it's time for the "Top Gun" star, 57, to step into character roles, and stop risking his health.
Cruise, who played Reacher in two films, shattered his ankle while performing a rooftop jump on the London set of the last "Mission: Impossible" movie, and Child fears his next injury could wreck his career.
"He's too old for this stuff," the writer told The Sunday Times. "He's 57, he needs to move on, transition to being a character actor... He could get another 20 years out of it. He has the talent. He's a terrific guy, very considerate, good fun."
Child previously caused a stir when he suggested Tom was a poor choice for Reacher, because he didn't have the "physicality" of his character.
"I really enjoyed working with Cruise," Lee added. "He's a really, really nice guy. We had a lot of fun, but ultimately the readers are right - the size of Reacher is really, really important and it's a big component of who he is."