The European Council president warned Mr Johnson could go down in history as "Mr No Deal" before the prime minister had even touched down.
But speaking on the plane to Biarritz, Mr Johnson retaliated by suggesting a failure to reach a Brexit agreement would also reflect badly on Mr Tusk.
The prime minister is preparing for his first international summit and meeting with US president Donald Trump since he entered Downing Street.
Ahead of the summit, which continues until Monday, Mr Johnson warned his Brexit critics they were “gravely mistaken” about the UK losing its place on the world stage.
Welcome to live updates from The Independent on the three-day G7 summit in Biarritz, France.
Boris Johnson was preparing for his first international summit and trade talks with Donald Trump.
The meeting of leaders from major economies in Biarittz will see Mr Johnson set out his plans for Brexit in talks with Donald Tusk, the president of the European council.
Ahead of the summit, Mr Johnson said: "Some people question the democratic decision this country has made, fearing that we will retreat from the world. Some think Britain's best days are behind us.
"To those people I say: you are gravely mistaken."
Mr Johnson and Mr Trump spoke by phone on Friday evening ahead of the meeting. It was their fourth official phone call since Mr Johnson entered Downing Street a month ago and the second call this week.
A Downing Street spokesman said: "They discussed topics on the agenda for the summit, including foreign policy issues and global trade."
Jeremy Corbyn, the Labour leader, has warned Mr Johnson not to push Britain into a "Trump first" Brexit as the prime minister heads for his first face-to-face meeting with the US president. Andrew Woodcock, our political editor, has the story:
Leaders of the G7 nations will meet amid a brewing confrontation between the US and China over protectionism.
Emmanuel macron, the French president, will have a tough task of delivering meaningful progress on trade, Iran and climate change.
Mr Macron wants the leaders of Britain, Canada, Germany, Italy, Japan and the United States to focus on the defence of democracy, gender equality, education and climate change, and has invited leaders from Asia, Africa and Latin America to join them for a global push on these issues.
But with the trade war between China and the US escalating, European governments struggling to defuse tensions between Washington and Tehran and global condemnation growing over illegal fires in the Amazon, his agenda could be eclipsed.
Mr Trump's history of belligerence towards multilateral gatherings, which brought last year's G7 summit to an acrimonious conclusion, means there is little hope for substantive agreements.
France has already decided that, to avoid another failure, there will be no final communique.
Mr Trump's walkout at the Charlevoix summit in Canada last year prompted foreign policy observers to dub the Group of Seven nations the G6+1.
Boris Johnson will urge world leaders to take tougher action on climate change and environmental protection, Andrew Woodcock, our political editor writes, as the prime minister announces a cash boost for research into flying taxis and delivery drones.
On Friday, EU leaders piled pressure on Jair Bolsonaro, the president of Brazil, over fires raging in the Amazon rainforest.
Mr Macron, the French president, said Mr Bolsonaro had lied in playing down concerns about climate change at a G20 summit in Japan in June, and threatened to veto a trade pact between the European Union and the Mercosur bloc of South American countries.
Greenpeace called the deforestation an emergency that highlighted the G7 leaders' need to act on ending fossil fuels and protecting forests.
"Once again, Emmanuel Macron is making bold statements which have yet to be matched by actions," said Greenpeace France Executive Director Jean-François Julliard.
"France and other developed countries are responsible for the dire Amazon situation through their economies and contribution to imported deforestation, fuelled by ill-designed policies in sectors like agriculture, timber and bio-energies."
Hours before leaving for Biarritz, Mr Trump reacted angrily to China's move to impose retaliatory tariffs on more US goods, even saying he was ordering US companies to look at ways to close their operations in China.
The president cannot legally compel US firms to abandon China immediately.
"Our Country has lost, stupidly, Trillions of Dollars with China over many years," Mr Trump tweeted. "We don't need China and, frankly, would be better off without them."
Xi Jinping, China's president, is not among the Asian leaders invited to the Biarritz summit.
Here's more on how US allies have nearly given up on the idea the G7 summit will produce unity and consensus:
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