The Fateh al-Sham Front, formerly known as Al-Nusra Front, is the most powerful faction in Syria's northwestern province of Idlib, which remains largely beyond the control of the regime.
It heads the Hayat Tahrir al-Sham coalition, which brought together an array of sympathetic rebel and jihadist groups and holds sway across Idlib after ousting rival factions earlier this year.
But the coalition has been hit by successive defections in recent months, leaving Fateh al-Sham isolated just as neighbouring Turkey appears to be readying an offensive against the jihadists with help from Syria rebel fighters.
"People used to adore Al-Nusra, but now they're waiting for the Turkish army to enter and finish them off," an opposition activist told AFP on condition of anonymity.
On Saturday, Turkish President Recep Tayyip Erdogan announced that Syrian rebels would stage a military operation in Idlib "to ensure security".
The operation is linked to a deal agreed earlier this year by rebel backer Turkey and regime allies Russia and Iran to implement four so-called "de-escalation zones" in Syria.
Under pressure and increasingly weak, most rebel groups have acquiesced to the ceasefire zones, but Tahrir al-Sham fiercely opposes it.
A Syrian rebel commander told AFP on Saturday that the Ankara-backed operation in Idlib aimed to drive Tahrir al-Sham from the entire province.
- Wave of defections -
Tahrir al-Sham, which is listed by the US and others as a "terrorist" group, counts an estimated 10,000 fighters among its ranks, according to the Syrian Observatory for Human Rights monitor.
It is the regular target of regime and Russian air strikes, with Moscow alleging this week that the group's leader Abu Mohamed al-Jolani was seriously injured in a raid, a claim the group denied.
And it has seen its ranks rapidly depleted in advance of the expected Turkish operation, with its coalition now effectively reduced back down to Fateh al-Sham.
Ahmed Abazeid, a Syrian researcher at the Turkey-based Toran Centre, said the Tahrir al-Sham coalition was always "essentially a sham".
"The decision-making and leadership remained in the hands of Al-Nusra Front," he added.
"A Turkish intervention has been on the table for a long time," he said, adding that Turkey had been working to encourage defections in order "to isolate the group associated with Jolani".
The first move, however, came from Tahrir al-Sham's side, with the jihadists in July launching a massive assault on its most powerful ally, Ahrar al-Sham, and evicting it from all but a few parts of Idlib.
Soon after, the prominent Nureddine al-Zinki faction abandoned Tahrir al-Sham, and at the end of September, the faction serving as the coalition's elite force, Jaish al-Ahrar, also jumped ship.
They cited "the increasing number of painful internal incidents", and their departure prompted further defections from Tahrir al-Sham.
- Jihadists seen as 'risky' ally -
The schisms and defections mean Tahrir al-Sham "has shrunk and is now confined to its primary component", said Sam Heller, a Syria expert at the Century Foundation think-tank.
He said the defections could be read as "opportunistic in anticipation of a Turkish intervention".
Charles Lister, a Syria expert at the Middle East Institute, said the conflict had "entered a new stage", with jihadists now seen as a toxic ally for rebel groups.
"Being attached in any way to groups like Tahrir al-Sham is becoming an increasingly risky choice," he said.
"Syrians are being forced to embrace a more pragmatic approach to their revolution."
Tahrir al-Sham, however, has indicated little interest in compromise, with the group's leadership making it clear "that they would fight to the death against any external intervention", he added.
An uptick in Russian and regime strikes on Idlib in recent weeks has already resulted in a soaring civilian death toll and fears that the upcoming confrontation could prove extremely bloody.
Internally, meanwhile, Tahrir al-Sham is facing additional divisions, said Abazeid.
On one side is a "current that believes it is necessary to engage with Turkey and other countries and no longer be designated" a terrorist group, he said.
But a more hardline Al-Qaeda current opposes any compromise and wants to "confront Turkey and the remaining rebel factions... and considers that moderation brings no results".