PKR president Anwar Ibrahim has scheduled a press conference at 12pm today to make "an important announcement".
Speculation is rife that the Port Dickson MP has cobbled together enough MPs to have a majority in Parliament.
Quizzed on whether Anwar has the numbers, a source close to him said: "Yes."
Pressed further, he declined to reveal the exact number or details for now.
"But (it is a) large majority," he said.
It is unclear who Anwar has managed to get on his side, but there is speculation that this does not include former premier Dr Mahathir Mohamad's Pejuang faction or Warisan.
Pejuang senator Marzuki Yahya told Malaysiakini he was unaware of any development or whether his party is included in Anwar's numbers.
Instead, Anwar may have secured support from Umno lawmakers. A PKR source also indicated that he may have cinched Sarawak-ruling coalition GPS' backing.
Works Minister Fadhilah Yusof, however, denied any knowledge of this when contacted, and said he was heading for a Perikatan Nasional (PN) cabinet meeting.
Meanwhile, there are also rumours that Anwar might be seeking an audience with Yang di-Pertuan Agong Sultan Abdullah Sultan Ahmad Shah.
Yesterday it was reported that the King was undergoing treatment at the National Heart Institute, but would be discharged soon.
However, as of writing, the Agong is still in the hospital.
At present, PKR, DAP, and Amanah have 91 seats.
Warisan, Upko and Pejuang have 15, while Parti Sarawak Bersatu (PSB)'s two MPs and independent Muar MP Syed Saddiq Syed Abdul Rahman are also not aligned with the PN government.
Combined, this current opposition block has 109 seats. If Anwar has support from GPS, this means they have 127 - a majority of 16 seats.
However, if Anwar doesn't have Warisan and Pejuang's support, he can still form a government with 112 seats if he has the backing of PSB and Syed Saddiq.
Otherwise, the PKR president must secure defectors from PN.
Regardless of whether he has a strong majority or not, the Federal Constitution puts the power in the hands of the Agong to decide whether to ask a prime minister who has lost support to resign, or to dissolve Parliament.