Lajim was referring to a convention of Pakatan Harapan (PH) that chose to name Tun Dr Mahathir Mohamad as its interim prime ministerial candidate on Sunday, in the event the opposition coalition wins the imminent general election.
Due to his conviction, Anwar can not stand for election over the next five years unless he is pardoned by the Malaysian King.
"In my opinion Tun Mahathir would only use his position as a stepping stone to prepare his son Datuk Seri Mukhriz as PM, as history has shown he fired his deputies for power when he was PM".
With the country's most popular opposition leader Anwar Ibrahim in jail, Mahathir is seen as the biggest threat for premier Najib Razak, who must call an election by August but is engulfed in a corruption scandal.
Mahathir, who during his 22-year tenure as prime minister earned a reputation of being a no-nonsense authoritarian with little time for dissenters promoting liberal values, stands to become the world's oldest leader if the opposition wins.
The decision to pick Mahathir as candidate was endorsed by senior leaders of the four-party coalition, Pact of Hope, at their convention outside of Kuala Lumpur, rousing cheers by hundreds of supporters.
"He (Mahathir) may start giving conditions, and the person taking over will just nod at anything but later, will not fulfil what has been agreed upon", Lajim said.
Malaysia's opposition leader Anwar Ibrahim is expected to be released from prison on June 11, an event that is likely to have implications for the country's political temperature.
If the opposition wins, the parties said they will ask for a royal pardon for Ibrahim so that he is eligible to become the prime minister. But the then Prime Minister also restrained freedom of expression and oversaw a rise in cronyism.
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He can not run for political office for five years after his release unless he is pardoned by the King.
Surprisingly, the Selangor chapter of Anwar's Parti Keadilan Rakyat (PKR) is also against Dr Mahathir's nomination.
This is the first time anyone has given an actual date for Anwar's release after serving a five-year sentence for sodomy.
"The main goal now is to topple UMNO and Najib", Mahathir told journalists on Sunday. Soon afterwards, Anwar was jailed on charges of sodomy and graft, after being sacked as the deputy prime minister.
Anwar, now serving a five-year sentence for sodomy, is due to be released from prison on June 8, the Prisons Department director-general said on Sunday, barring any intervention from higher authorities.
A political observer said although Dr Mahathir brought invaluable experience to the opposition table, the former premier was associated with many controversies and scandals that plagued his administration.
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.
The fund has denied any wrongdoing and Najib, who founded 1MDB, has denied all allegations of corruption against him and was cleared of wrongdoing by Malaysia's attorney-general.