According to a Reuters report, Tierney, 44, had to pull out of the show because of scheduling conflicts between filming for the series and her breast cancer treatments.
The show, based on the 1989 Ron Howard film, was to have made its debut at the start of the 2009-10 season but was pushed back to mid-season when Tierney's doctors found a tumour in her breast.
With the treatment taking longer than expected, NBC would now be recasting the role.
