Kelly appeared in the first two seasons of the show as Gaby before leaving to star in ABC's remake of Charlie's Angels.
The series was recently cancelled, but Katims has now told TV Line that he is not expecting Kelly to return.
"I would love to bring the character back," he said. "But since we've already broken the stories for this season, I think it's unlikely that could happen."
Life Unexpected star Rafi Gavron recently signed up for a role in the current season of Parenthood, which has been extended by two episodes.
The show airs on Tuesdays at 10/9c on NBC.