By John Young
Updated July 10, 2009 at 12:00 PM EDT

NBC has pushed the debut of its new drama series Parenthood from Sept. 23 to sometime midseason (typically November to February) due to an unspecified medical matter involving star Maura Tierney, 44, according to a statement NBC released July 10. The show, which is based on the 1989 movie starring Steve Martin, was scheduled to begin production on July 27, but its start date has been pushed back eight weeks due to a “medical evaluation that Tierney is undergoing.”

Parenthood depicts the relationship between four siblings (Tierney, Peter Krause, Erika Christensen, and Dax Shepard) and their parents (Craig T. Nelson and Bonnie Bedelia). The new medical drama Mercy will take Parenthood‘s spot this fall.

NBC would not comment on the nature of Tierney’s illness. A rep for the ER actress had no comment.