The chief of Calais port warned today Britain faces "disaster" if Mr Macron blocks British trawlers from French ports.
France last night begged the rest of the EU to join its fishing war against Britain as a punishment for Brexit.
French PM Jean Castex said Brussels must sign up to its campaign against the UK to keep the bloc together.
Mr Macron’s sabre-rattling deputy wrote an explosive letter to chief Eurocrat Ursula von der Leyen urging her to act.
The G20 summit kicks off today four months after Mr Macron and Mr Johnson clashed at the G7 summit over Brexit.
Asked by The i about meeting the French leader again, Mr Johnson said: "It’s about fish rather than sausages this time, I don’t know if that’s an improvement.
"Actually, there are bigger fish to fry, everybody knows that. Am I worried about that?
"The answer is no."
Speaking this morning, Mr Johnson warned Britain could trigger legal repercussions in the post-Brexit trade agreement next week over the row.
If France breaks the Brexit trade deal “then obviously we will have to take steps to UK interests”, the PM told Sky News.
Asked if he would rule out triggering the dispute resolution mechanism next week, Mr Johnson said: “No of course not, I don’t rule that out.”
In his letter to Brussels bigwig Ursula von der Leyen, Mr Castex said: “It is essential to clearly show Europeans honouring commitments is non-negotiable and there is more harm from leaving the EU than remaining.”
The threat sparked fury in Downing Street and a backlash from Tory MPs.
Anthony Mangnall, for the fishing community of Brixham, hit back: “This is completely unacceptable.
“The French should not be behaving in this manner.
“We are happy to work with them but not if they behave in this way.”
Germany and Brussels have already slapped President Macron down and urged him not to drag the EU into a fresh spat.
The French leader has raised tensions further by claiming the fishing row is a test of Britain's global credibility and accused Britain of backtracking over Brexit commitments.
He told the Financial Times: "When you spend years negotiating a treaty and then a few months later you do the opposite of what was decided on the aspects that suit you the least, it is not a big sign of your credibility."
Meanwhile, as authorities across the Channel charged a British skipper for fishing in their waters without a licence, Boris Johnson vowed to do “whatever is necessary” to protect our fisherman from the French.
NAVY ON STANDBY
And the Royal Navy was put on standby.
In May, the PM dispatched two Navy patrol boats, HMS Severn and HMS Tamar, to protect Jersey after French vessels blocked the port.
He will now tell Mr Macron today to rein in his gobby ministers to avoid an all-out fishing war as the two leaders come face to face for a showdown at the G20 summit.
As tensions threaten to boil over, the PM said he would try to force the French president to step back from the brink. But he warned the swaggering French that he stands ready to do whatever it takes to protect our fishing vessels.
And raging UK ministers have threatened to mire French fishing vessels in red tape — including forcing them to land their catches on our shores — if Paris refuses to back down.
Done like a s-kipper
From Amir Razavi, in Le Havre, France
FRANCE sparked more fury yesterday as an impounded British scallop trawler’s skipper was charged with “unauthorised fishing”.
As the bitter cross-Channel trade war escalated, he was trapped on the vessel with his crew — not knowing when they will be freed.
The bearded man, bemused by the publicity, was served a summons but will not appear in court until next August — and faces a £63,000 fine if convicted.
It is claimed his Cornelis Gert Jan vessel fished in the French exclusive economic zone without a licence.
The crew have been told to remain on the boat in Le Havre, “for their own safety”.
One grinned as he collected Union Jack mugs and a bottle of Scotch from supporters.
The highly controversial move comes after Foreign Secretary Liz Truss summoned the French ambassador Catherine Colonna to her office and Paris blasted the Government.
Speaking on the plane to Rome last night, Mr Johnson said: “We will do whatever is necessary to ensure UK interest.” The PM vowed to confront Mr Macron in Rome today and will urge his counterpart to remember Britain is a close ally of France — not an enemy.
But in a swipe, Mr Johnson said: “We fear there may be a breach of the terms of the trade cooperation agreement.” He added: “Obviously, we will stand by to take the appropriate action.”
He and Mr Macron are meeting, along with US President Joe Biden, to discuss the crisis in Iran.
The pair will then meet again on Sunday when Mr Johnson is expected to confront Mr Macron about France’s behaviour.
Environment Secretary George Eustice, meanwhile, warned “two can play at that game” as he threatened ban French boats and bind its trawlermen in red tape.
He also suggested Mr Macron had allowed the fishing wars to flare up to play to nationalist French voters ahead of next year’s election.