Am I mistaken, or did John Ritter guest star on Newsradio? If so, what seasons did he guest star, and how many episodes was he in?

He guest starred in a season two episode "The Shrink". He plays a psychiatrist that comes in to help out the staff. It turns out Lisa and Ritter's character are past lovers from when he was her therapist. Dave feels uncomfortable working with his girlfriend's ex-lover.

He was only on the show this once. He appears in a gag reel scene on the DVD.