EU leaders have repeatedly called for the Ukrainian’s release since he was sentenced by a Russian court to 20 years in a high-security prison for “terrorist attacks” in Crimea.
Mr Sentsov began his hunger strike in May ahead of the World Cup in an effort to highlight Russia’s dismal human rights record, calling on Moscow to release all Ukrainian political prisoners.
He pledged to continue his strike until his demands are met.
Earlier this week, his lawyer, Dmitry Dinze, told the AFP news agency that his client, who is being sustained with water and a drip with glucose and vitamins, had lost around 30kg.
Mr Dinze added that the Ukrainian’s heart rate had slowed and that he was suffering from anaemia.
Mr Macron has discussed the fate of Mr Sentsov with Mr Putin more than once, including during a visit to Saint Petersburg in May.
Mr Sentsov, 42, is serving a 20-year sentence in a high-security penal colony in northern Russia after being found guilty of organising a terrorist group in his native Crimea in a bid to free it from Russian rule.
He was accused of setting fire to two office buildings in Crimea, including one occupied by Russia’s ruling party, and of plotting to blow up a monument to former Soviet Union leader Vladimir Lenin.
The anti-Kremlin activist pleaded not guilty and repeatedly claimed his 2015 trial was politically driven.
Western leaders, led by Mr Macron, have since urged Russia to release Mr Sentsov, to no avail.
The European Union said the Sentsov case was “in breach of international law and elementary standards of justice;” while the US State Department denounced the sentence as a “clear miscarriage of justice”.
Amnesty International condemned a “show trial,” which they said was riddled with irregularities.
On Wednesday, Mr Sentsov’s cousin, Natalya Kaplan, said on Facebook that he was in a “catastrophically” bad state.
“He can’t get up. He writes that the end is near, and he’s not referring to when he will be freed,” she said.
Amnesty International said earlier this week that its request to visit Mr Sentsov together with medical experts had been denied.
“The Federal Correctional Service told us that his health is stable and that they see no changes for the worse. But that information is two weeks old. Sadly, we know as little as everyone else,” Amnesty Russia’s Aleksander Artemev said.