Labor, Social Services and Social Equality Minister Itzik Shmuli announced on Tuesday evening that he would not run in next Sunday's Labor leadership primary.
In a post on Facebook, Shmuli warned that the Labor primary could prevent the political mergers needed to unseat Prime Minister Benjamin Netanyahu.
In his message, Shmuli hinted that he would not remain in the Labor Party, and would be running on a different slate. Sources close to him said he would reveal his new political home very soon.
Former prime minister Ehud Barak wrote on social media on Monday night that he would not accept requests from Labor activists to run.
The candidates who have declared they are running are MK Merav Michaeli, advertising executive Gil Beilin, online casino millionaire Avi Shaked and activist David Landsman. Michaeli is now the clear front runner. If elected, she may be the only women leading a party in the election.
The deadline to join the race is Thursday.