Israel's prime minister contender Gantz races to form government
Netanyahu's right-wing Likud party and Gantz's centrist Blue and White coalition achieved near parity in September's repeat elections, but even with allied parties both fell short of the 61 seats needed to form a majority in parliament.
Netanyahu was first given 28 days to form a coalition government but failed, so President Reuven Rivlin granted Gantz a similar timeframe.
It is due to expire at 11:59pm on Wednesday, and the former army chief has been engaged in a negotiation blitz in a bid to avoid a third general election in a year.
Polls in April also led to a stalemate in a political system reliant on coalition building.
Gantz's task may have been further complicated by a flareup between Israel and Islamic Jihad in the Gaza Strip last week, as his potential premiership likely rests on Arab support in parliament.
Gantz has been desperately trying to convince Avigdor Lieberman, head of the nationalist Yisrael Beitenu party, to join his coalition.
But even if he did they would fall short of a majority - needing at least the tacit support of the Arab Joint List, which has 13 seats, to govern.
The Arab parties would be unlikely to take ministries but could support a minority Gantz government in key votes in Israel's parliament, the Knesset.
But Lieberman, a right-winger known for his tough rhetoric towards Gaza, has reiterated his opposition to allying with Palestinian-Israeli politicians.
The former nightclub bouncer has been a defiant kingmaker, with his eight parliamentary seats potentially enough to put Netanyahu or Gantz into power.
Netanyahu, facing losing office for the first time since 2009, has upped his anti-Arab rhetoric in a seeming bid to increase pressure on Lieberman.
Arab Israeli members of parliament [Getyy]
On Sunday he warned of a "dangerous government" backed by parties that "support terrorist organisations".
Gantz, Lieberman and Netanyahu all supported the Israeli assassination of an Islamic Jihad leader in Gaza that prompted a deadly flareup last week, while the Joint List opposed it.
"The Arabs... are not Zionists and do not support Israel. To be dependent on them all the time, especially at the present time, is an enormous danger to Israel," Netanyahu said during a demonstration against a minority government.
Gideon Rahat, a political science professor at the Hebrew University in Jerusalem, said negotiations were likely to go down to the final moments.
"(Gantz and Netanyahu) are playing games, trying to pressure each other," he said.
"There are a lot of rumours, and it is a game of pressure - so I don't know what the end result will be."
Israeli Arabs are the descendants of Palestinians who remained on their land when Israel was created in 1948 and constitute nearly a fifth of the country's population.
They have full legal rights but complain of discrimination and incitement against them in the predominantly Jewish country.
|An indictment might permanently damage Netanyahu's support, whereas a reprieve could give him a new lease of life|
A range of scenarios remain and are likely to be played out in frantic negotiations behind closed doors.
Lieberman could ultimately backtrack and cut a deal with Netanyahu, or he could throw his weight behind Gantz and form a minority government.
"Does Gantz himself want to lead such a government? The answer is no," a columnist in the Israeli newspaper Haaretz said Monday.
And Lieberman, it added, "certainly doesn't want any form of partnership with (the Arabs). But does he have a better option?"
If Gantz is unable to cut a deal by Wednesday, lawmakers have 21 days to propose a candidate capable of forming a majority to the president.
There is also a joker in the pack - with Attorney General Avichai Mandelblit expected to decide by December whether to charge Netanyahu over corruption allegations he denies.
An indictment might permanently damage Netanyahu's support, whereas a reprieve could give him a new lease of life.
If the 21 days pass without a breakthrough, a third election becomes inevitable.