Maverick politician Rafizi Ramli plans to contest the deputy president's post in Parti Keadilan Rakyat (PKR), a move that has laid bare the tensions between the ruling party's two rival factions.
PKR, the biggest party in Malaysia's ruling alliance Pakatan Harapan (PH), will hold its triennial polls at the end of next month.
PKR's de facto leader, Datuk Seri Anwar Ibrahim, has indicated that he plans to contest the No. 1 post to replace his wife, PKR president Wan Azizah Wan Ismail, who is Malaysia's Deputy Prime Minister.
The No. 2 post that Mr Rafizi is eyeing is held by Economic Affairs Minister Azmin Ali, who heads one PKR faction. Mr Anwar and Mr Rafizi are from the party's other faction.
Founded two decades ago following the sacking of Mr Anwar from Umno, PKR today has 50 MPs in the federal Parliament - the largest number among the four PH member parties.
"Yes, I confirm that I will be running," Mr Rafizi told news site The Star Online on Thursday.
The move by Mr Rafizi, a PKR vice-president, will force Mr Azmin to either defend his post or contest against Mr Anwar for the president's post.
In response to Mr Rafizi's announcement, Mr Azmin's political secretary, Mr Muhammad Hilman Idham, told Malaysiakini news site that Mr Azmin welcomed the contest as the party is "always up for healthy competition, as long as slander is not involved".
But party insiders and observers fear tensions between the two factions might now turn openly hostile.
Said political analyst Wong Chin Huat: "It would be a baptism of fire to see if the party can remain intact after a bitter contest."
He added: "If Azmin wants to play safe, he might want to just take on Rafizi. Rafizi is popular outside of the party but may not be so in the party. If Azmin wins handsomely, his position as Anwar's heir would be unchallengeable and Anwar's premiership may be just a term plus before (he passes) the baton to Azmin."
Mr Anwar, currently PKR's unelected ketua umum, or de facto chief, is contesting the president's post as he gears up to become Malaysia's prime minister in around two years' time to replace Tun Dr Mahathir Mohamad, as agreed on by PH's leaders.
If Mr Anwar wins the president's post, he would next contest a by-election to become an MP, allowing him to be appointed the country's eighth prime minister.
Mr Azmin has yet to announce whether he would contest the No. 1 or No. 2 post, amid calls by his allies urging party members to allow him to lead the party.
Housing and Local Government Minister Zuraida Kamaruddin, an Azmin ally, said the Economic Affairs Minister is a dynamic leader who is capable of leading PKR.
Mr Azmin's stature has grown in recent years since becoming Selangor's Menteri Besar in 2014 while Mr Anwar was in jail.
After the May 9 general election, Dr Mahathir unexpectedly appointed Mr Azmin as a Cabinet minister and assigned a raft of agencies and state enterprises to his care.
But should Mr Azmin stand against Mr Anwar and lose, he will likely be cut off from the PKR leadership, with Mr Rafizi instead in position to succeed Mr Anwar.