Mad Men actress Elisabeth Moss has taken aim at Jeremy Piven over his decision to quit a 2008 Broadway play over a bad bout of mercury poisoning, branding him "highly unprofessional".

The Entourage star exited a production of David Mamet's play Speed-The-Plow less than two months into the run after falling ill and producers subsequently hired William H. MACy to take over the role.

However, Piven's one-time co-star Moss was far from impressed by Piven's decision to leave the production, admitting she was "surprised" by his sudden departure.

During an appearance on Andy Cohen's Watch What Happens Live on Thursday (23May13), the Tv host asked Moss, "What, besides eating too much sushi, caused Jeremy Piven to quit Speed-the-Plow?"

She replied, "That's a very good one. I could go on and on. Being highly unprofessional. We were all surprised. It came out of nowhere. He just didn't come back one day.

"I saw him like a month later at the Golden Globes... when he was supposed to be really sick."