According to The News Journal of Wilmington, the Republican told reporters Wednesday that he probably would not run, but has not ruled it out.
Tea party darling Christine O'Donnell upset Castle in the Sept. 14 primary to snag the Republican nomination in the race to fill the Senate seat once held by Vice President Joe Biden.
Castle has until Sept. 30 to declare his candidacy in writing at the state election office for his votes to be counted.
Castle says he "will consider it right up until the final moment" but that he's "not headed in that direction right now."
Information from: The News Journal of Wilmington, Del.