"That is why we are calling him again today (Aug 7) to record his statement for tomorrow's proceedings", a source told The Star.
Jho Low's yacht, the Equanimity has pulled into Indonesia's Batam Island, where it will await a transfer of hands from Indonesian to Malaysian authorities.
Najib said the government should now remain focused on finding ways to repay the huge debt still owed to International Petroleum Investment Corporation (IPIC), instead of trying to sell the yacht off to the highest bidder.
USA investigators said Low, known widely as Jho Low, bought the yacht with proceeds diverted from 1MDB.
In a 2 minute 35 second video posted on his Twitter account, the prime minister said the yacht belonged to Malaysia as it was purchased with Malaysian money that was stolen by "certain quarters".
The US$250 million Equanimity arrived this morning at Port Klang, courtesy of Indonesian police who seized the yacht in May in Bali.
Indonesian police seized the boat again in July 9 following a formal request for legal assistance from the United States.
Malaysian authorities have issued an arrest warrant for Low, whose whereabouts are unknown. He and the fund have denied any wrongdoing.
The Malaysian state fund is at the centre of money-laundering probes in at least six countries, including the United States, Switzerland and Singapore.
The scandal led to the stunning electoral victory in May by a coalition led by the 92-year-old Mahathir over Najib's National Front coalition, which had ruled Malaysia uninterrupted since gaining independence in 1957 - 22 of those years under Mahathir himself.
The US Department of Justice has said more than $4bn was misappropriated by high-level officials from the fund and their associates.
Dr Mahathir has said anyone who wants to claim ownership of the yacht must show proof that the vessel was not bought with stolen funds.