The French daily spoke to three men who have fought alongside Ukrainian ground forces. It said the numbers could not be independently verified.
The fighter identified as Pierre estimated that only a third of foreign fighters had military training before coming to Ukraine. Many joined the fray in search of "adventure and adrenaline."
"It's a lifestyle they look for, an unconventional one. But not just in any country. Ukraine seems like an obvious cause," Pierre said.
The French are a minority, the man admitted, adding this made him feel disappointed. He said the conflict could draw out.
Fewer fighters have reportedly been going to Ukraine in recent months, despite Ukraine's preparations for a much-touted spring offensive, and some of those coming home face criminal investigation.
Many European countries have a ban on foreign fighting in place. France views cases of its nationals who are foreign fighters on a case-by-case basis. Two Frenchmen have been arrested after returning to France this month on suspicion of involvement in extremism.