Tim Daly is set to guest star in the "enhanced" two-hour episode of ABC's 'Grey's Anatomy,' designed to serve as backdoor pilot for a planned new series, reports Reuters. Paul Adelstein, currently on Fox's Prison Break has also been cast as a guest star in the episode, with a possibility of appearing in the potential spinoff headlined by Kate Walsh. Last week, Taye Diggs announced he would also be joining the cast of the new show.

As plans firm up for Untitled Medical Drama, fans of the current show may start worrying. While spinoffs don't always eat their own, the attention of the showrunner on his or her new darling often has negative effects on the first series. In a case of series sibling rivalry, either the two programs will complement each other, or else the younger will take the eye of the "parent" off the older, leaving fans with headaches like Buffy's sixth season, or the second season of Sports Night.