Piven (right) had been expected to stay in the show until late February
The doctor who told actor Jeremy Piven to pull out of a Broadway run of David Mamet's Speed-the-Plow has hit back at comments made by the US playwright.
After being told Piven was leaving the show due to a high mercury count, Mamet joked the 43-year-old could now "pursue a career as a thermometer".
Dr Carlon Colker, though, said the jibe was "insensitive... unkind and unfair."
Two actors have agreed to step in for Piven, best known for playing agent Ari Gold in hit US TV series Entourage.
Tony award-winner Norbert Leo Butz will take his role from 23 December to 11 January, with Mamet regular William H Macy covering the rest of the run.
'Lack of understanding'
Dr Colker, an attending physician at Beth Israel Medical Center in New York, suggested Piven's high mercury count could have been caused by a combination of fish and Chinese herbs.
"He needs convalescence and rest and treatment," the medic told trade paper Variety. "This will clear his body and he will be back in action very soon."
Comments like Mamet's, he continued, "reflect a profound lack of understanding of a problem that can actually kill."
"Jeremy has been a trouper and did everything he could to fight extreme fatigue, among other things."
First staged in 1988, Speed-the-Plow tells of a Hollywood executive and his relationships with a struggling movie producer and an idealistic young assistant.
Kevin Spacey and Jeff Goldblum appeared in a London production of the play at the Old Vic earlier this year.