The announcement came amid preparations for the general election by both the ruling Barisan Nasional (BN) coalition led by Prime Minister Najib Razak, and the four-party PH opposition alliance helmed by ex-premier Tun Mahathir Mohamad, 92.
Mr Najib's coalition lost the popular vote in that election, but won a majority of the seats in parliament.
Ti said when Pakatan Harapan decides to name them their future Prime Minister and Prime Minister-in-waiting shows it is not serious about the change they have been promoting and promising the people.
Mahathir's ascent to opposition prime ministerial candidate is the latest sign of how dramatically Malaysia's political landscape has been shaken up by a massive financial scandal that has rocked Najib's government.
The final report by the official Royal Commission of Inquiry into the scandal in the 1990s during Mahathir's tenure also recommended Anwar Ibrahim - finance minister at the time and now a leading opposition figure languishing in jail - face a criminal probe.
Lajim who is also the State's opposition leader said he could not comprehend Dr Mahathir's stand when he had mentioned of retiring from politics and yet does not mind being named as the prime ministerial candidate after leaving the post nearly 20 years ago.
Mr Anwar was convicted and jailed again in 2013 for sodomy, a charge he says is an attempt to end his career. "It's cruel for [the Justice Party] to have Mahathir", Zuraidah Kamarudin, the party's women chief was quoted as saying in local media. In a November survey by the Merdeka Center of Opinion Research, 72% of respondents named economic hardship as their top concern.
He also felt that the party's decision was probably also motivated by the belief that Mahathir still had the capacity to influence the Malays in West Malaysia.
Mr Najib, 64, is now unassailable in his party Umno and in the 13-party BN coalition, after locally containing the scandal surrounding state fund 1Malaysia Development Bhd.
And Najib, who founded 1MDB and has denied all allegations of corruption against him, was cleared of wrongdoing by Malaysia's attorney-general.
Mahathir formed Bersatu a year ago and toured the country to garner support with the sole aim of unseating Najib, the only common ground that existed among a fragmented opposition alliance. And he is also mindful of overstaying his welcome.
"Dr Mahathir is sharp on policies and knows the workings of the government; Anwar will rally the urban crowd", said ISEAS-Yusof Ishak Institute fellow Norshahril Saat.
"But when he was nominated as the prime minister, and he has been a prime minister for 22 years and has left that post for more than 10 years, I feel that Pakatan Harapan's action is due to desperation", said Lajim. "I don't last forever".