The "disciplinary procedure" that would lead to Assad being deprived of his Légion d'honneur has been under way for several months, the French presidency told Le Monde newspaper on Monday.
Assad was awarded the distinction in 2001 by then president Jacques Chirac, just after taking over power from his father, Hafaz, who himself was awarded the Légion by president Valéry Giscard d'Estaing in 1976.
Chirac's relations with Bashar al-Assad seriously deteriorated when former Lebanese prime minister Rafic Hariri was killed by a car bomb, allegedly by Syrian agents, in 2005.
But Franco-Syrian relations revived again under president Nicolas Sarkozy, who made Assad his guest of honour at the Bastille Day celebrations in 2008.
They have been troubled since the Syrian civil war broke out in 2011.
Despite calling for world powers to talk to Assad during last year's presidential campaign, Macron has taken a tough line and joined the US and the UK in last weekend's air strikes on alleged chemical weapons facilites in his country.
Chemical weapons inspection
The French presidency on Tuesday warned that it was "highly likely that evidence and essential elements will disappear from the site, which is completely controlled by the Russian and Syrian armies" after it was announced that international inspectors would be allowed access to Douma on Wednesday.
Russia has denied trying to obstruct the investigation and said the inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW), who arrived in Damascus on Saturday, were due to visit Douma on Wednesday.
The French foreign ministry said it was "essential that Syria give full, immediate and unimpeded access to all the OPCW's requests, whether relating to sites to visit, people to interview or documents to consult" in a statement.
The warning came as the US ambassador to the OPCW, Ken Ward, said Moscow might already have "tampered with" evidence at the site.
Russian Foreign Affairs Minister Sergei Lavrov rejected the allegation, telling the BBC: "I can guarantee that Russia has not tampered with the site."
He accused the US, France and Britain of "standing in the way" of the investigation by ordering air strikes "in the blink of an eye" before the OPCW team had a chance to do their work.
Syrian state media said the inspectors had entered Douma on Tuesday.
Aid package promised
France is to donate 50 million euros to projects in Syria, Macron's office announced on Monday after the president had met aid groups working there.
The projects will focus on the Idlib region, where an estimated 1.2 million displaced people live, in Ghouta region and in north-western areas recently liberated from the Islamic State armed group.
The UN estimates that 13 million Syrians, including six million children, need humanitarian aid.
The French parliament debated the air strikes without a vote on Monday.
Prime Minister Edouard Philippe told MPs they were "completely justified" adn "careully proportionate".
Left-wing and right-wing opposition members cast doubt on their legality and raised fears they would undermine France's standing in the Middle East.
Macron told the European parliament on Tuesday that they "solved nothing" but "end a system to which we are becoming used to, which is that, somehow, the right side has become the weak side".