Major General Kyrylo Budanov, Chief of the Defence Intelligence of Ukraine, made the claims in an interview with USA Today, adding to long-standing speculation about the Russian president’s health.
Citing what he called “human intelligence” from Ukraine’s spies allegedly operating out of the Kremlin, he claimed Putin “doesn't have a long life ahead of him”.
He estimated that he could only have two years left to live.
Putin is notoriously private and evidence for the claims of poor health have not been made public.
Last month Russian Foreign Minister Sergei Lavrov has been forced to deny Vladimir Putin is seriously ill after several reports he is being treated for blood cancer.
Answering a question from France’s broadcaster TF1, Mr Lavrov said at the time: “I don’t think that sane people can see in this person signs of some kind of illness or ailment.”
She added: “I leave it to the conscience of those who spread such rumours.”
In the interview, Mr Budanov also said that Ukraine’s military will soon score “obvious” wins in repelling Russia’s unprovoked invasion, and that two American volunteer fighters for Ukraine captured by Russian troops would likely be released within “a few months” in a prisoner swap.
Speaking from Kyiv, he predicted that if Ukraine continued to receive military aid, it will start scoring decisive “wins” in its four-month-old war with Russia that “will be obvious for the world community,” by mid-August.
Of the two US prisoners, Mr Budanov said: “We are working on it. The way of resolving it is not easy ... but we do see a way to resolve it.
“It will be more or less related to a prisoner swap.
“We have at our disposal people who the Russians want very much, who they need to get back very much ... but it also won't happen in a week or two. It will take a few months.”
It comes as the head of Nato said Monday the military alliance will increase the strength of its rapid reaction force nearly eightfold to 300,000 troops as part of its response to an “era of strategic competition”.
The NATO reaction force currently numbers around 40,000 soldiers which can deploy quickly when needed.
Nato Secretary-General Jens Stoltenberg said the move is part of the “biggest overhaul of collective defense and deterrence since the Cold War.”
Stoltenberg made the remarks at a press conference ahead of a Nato summit later this week in Madrid where further support for Ukraine is expected to be on the table.
Stoltenberg said he expects allies to make clear they consider Russia “as the most significant and direct threat to our security.”