Tun Dr Mahathir Mohamad, he said, will become Malaysia’s “de facto PM”, standing behind Najib.
He said the fall of Prime Minister Datuk Seri Abdullah Ahmad Badawi is a result of Dr Mahathir prevailing.
Zaid, who resigned recently from Abdullah's Cabinet in protest against the use of the Internal Security Act, said he did not expect Najib to continue Abdullah's reform agenda once he takes over.
"Legal and constitutional reforms make you less powerful, more accountable and less able to use the privileges of power.
"Why would someone trained and schooled by Dr Mahathir introduce reforms. Have you heard Najib speak of reforms?” he told The Malaysian Insider.
Zaid said he expects Najib's administration to be more authoritarian with more controls and restrictions compared to that of Abdullah's.
Abdullah, he said, believed in reforms, but "he did not have the stomach" to push through the changes needed.
During the interview he also responded to allegations made against him by Dr Mahathir on the latter's blog recently.
In his chedet.com blog, Dr Mahathir accused Zaid of being in Perth, Australia during the March general election, and for helping the Pas candidate win the Kota Baru constituency against the Barisan Nasional.
Dr Mahathir also criticised Zaid's move as minister to have the government institute ex-gratia payments to the judges who were sacked as a result of the 1988 judicial crisis.
Said Zaid in response: "He says I helped the Pas candidate, but the fact is Pas was going to win no matter what because of the anti-BN mood.
"He has conveniently forgotten that he actively asked the people to vote against BN to teach Abdullah a lesson."
Zaid added that Dr Mahathir would never be able to accept why ex-gratia payments were made to the judges because it reflects badly on his legacy as Prime Minister.
He said Dr Mahathir would never understand the need for reforms because, to him, "more authoritarianism is better”.
The former minister said Malaysia's political and economic uncertainties today is a result of Dr Mahathir.
He also blamed Dr Mahathir for Umno's unpopularity and lack of proper leadership.
"The truth is we have had no proper election since 1987," he said in reference to the year in which Dr Mahathir defeated Tengku Razaleigh Hamzah by a wafer-thin majority to retain the Umno presidency.
Soon after that election, Umno was declared illegal in a court case which led eventually to the 1988 judicial crisis and the sacking of judges involved in the case.
Under Dr Mahathir, the Societies Act was also subsequently amended disallowing judicial review of any political party decision.
"After the Societies Act was amended the president of Umno could do anything.
"You have destroyed the fabric of our lives as a democracy. Have you not done enough?''
Zaid said Malaysia faced an uncertain and more authoritarian future when Najib takes over.
"You had 23 years of Dr Mahathir, so let's say Najib lasts for 10 years as PM with Mahathir behind him. That means a total of 33 years under Dr Mahathir."
