The 39-year-old was found hiding behind a car and appeared drunk when he was spotted by police on patrol in Brittany on Saturday morning.
He was questioned a officers discovered that he was carrying a flick knife.
Under lockdown rules in France, people need to carry a certificate stating why they are leaving their homes.
According to CNN, the man had written on his permission form: "I've gone to smash a guy's face in. That's my excuse and it's a good one.”
Daniel Kerdraon, Lannion police chief, told the news website that officers explained to man this was not a legitimate reason and that he would be detained overnight.
He was reportedly fined €135 (£120) for breaching lockdown rules and another €150 (£130) for being drunk in a public space.
The report came as France prepared to ease its lockdown measures after the country recorded its lowest daily coronavirus infections since late September.
French President Emmanuel Macron laid out new rules on Tuesday in France's virus strategy, after imposing nationwide restrictions last month as virus infections and deaths surged around Europe.
