In an interview with the Telegraph, a senior Pakistani army source said the collapse in security since the draw-down of Western troops from Afghanistan meant the West now faced "losing control".
If Islamic State of Iraq and the Syria (ISIS) and the Taliban continued to gain strength, he added, it could tempt Russia to stage a Syrian-style intervention, this time on the pretext of protecting its "backyard" in Central Asia.
The source's comments will add to growing concern in Washington and London about the reversal of the hard-won gains made by coalition troops during 16-year-long Afghan campaign.
Districts of Helmand province, where more than 100 British troops died, have again slipped from Kabul's control, while in east Afghanistan, militants are regrouping under the ISIS banner.
Neighboring Pakistan was long accused of backing the Taliban and other militant groups through its powerful security establishment, which saw them as pawns to counter Indian influence.
But growing numbers of terrorist attacks on Pakistan itself has led to a change of heart, with the army launching massive operations in the last two years to clear extremists from its mountainous Afghan border.
With Islamabad now seeing itself an equal partner in the war on terror, Pakistan's generals fear their own efforts to fight militants - which have cost the lives of nearly 4,000 troops - will likewise be jeopardized by setbacks in Afghanistan.
Such claims may get limited sympathy in Washington. Last month, General John Nicholson, the head of US and Nato forces in Afghanistan, told Congress that certain Afghan militant groups, including the Taliban, still enjoyed sanctuary in Pakistan.
“It is very difficult to succeed on the battlefield when your enemy enjoys external support and safe haven,” he said.
The source within the Pakistani army, which has 180,000 troops on the Afghan border, said that in recent weeks, high-level discussions had taken place with both Gen Nicholson and James Mattis, the retired US general appointed by Mr Trump as Secretary of Defense.
Gen Nicholson himself admitted last month that Afghan forces - who are mentored by a scaled-down coalition force of 13,000 - were now in a "stalemate" against a resurgent Taliban.
The Pakistani source said even that was an "optimistic" assessment.
"A stalemate is still a win for the Taliban," he said. "We have told Gen Mattis that Afghanistan is slipping out of control, and that if things are not put right, America will have a huge crisis on its hands.
"ISIS is also developing there, and if they leave Syria and Iraq, the next place for them to gather in is Afghanistan."
Pakistan has criticized the Kabul government for not doing enough to seal its side of the Afghan border, from where Islamabad says militants are now launching attacks on both Pakistani and Afghan soil.
Last month, 88 people died in an attack on a religious shrine in Pakistan claimed by ISIS.
However, Islamabad admits that Kabul is limited by the capabilities of the Afghan National Army, which is part-trained by a 500-strong British troop contingent.
British claims about the success of its "Sandhurst in the Sand" program are not shared by Pakistan.
"There are 350,000 troops in the Afghan army, but only about 20,000 are capable of combat missions," said the Pakistani military source.
"They also have about 1,000 generals, most of whom are appointed because of their tribal affiliations rather than on merit."
As of yet, ISIS is just one of many jihadist players in Afghanistan, with perhaps less than 1,000 followers.
But its slick global franchising and exceptionally bloodthirsty nature makes regional security chiefs anxious.
The military source added that Russia feared the West was using ISIS as a "plot to destabilize its backyard", and rightly or wrongly, could use it as an excuse to extend military operations into Afghanistan.
Last month, Russia held a conference for regional powers on Afghanistan, signaling what could be the opening stages of such a strategy.
The summit, to which the US was pointedly not invited, called for dialogue with the Taliban, which Moscow has already started backchannel contacts with.
The Kremlin says the Taliban can be used to battle the more radical ISIS, an assessment described a "false narrative" by Gen Nicholson.
Washington believes that Kremlin-Taliban contacts are simply to help Moscow build proxy assets in Afghanistan.