Andrea Bonanni, of Italian publication La Repubblica, said Britain was “making things harder” for the EU before leaving by blocking legislation.
But he said it was all a ploy to win votes at the General Election.
He said: “From now until June 8, the day of the political elections in England, we expect a series of more or less reasonable attacks by British politicians who are obviously trying to win voters.
“Moreover, Britain over the last few weeks, contrary to what it had promised, has already blocked two decisions that the EU had to take, one on the budget and the other one on the creation of a European Office for Defence.
“So they are making things harder for the EU before leaving.”
The comments come after Mr Johnson told The Telegraph the EU should pay the “preposterous” Brexit bill.
He said: “There are assets, I don’t want to get too much into the detail of the negotiation but there are assets that we share, that we have paid for over the years and there will need to be a proper computation of the value of those assets.
“I certainly think the bill that’s been presented at the moment is absurd. They are going to try to bleed this country white with their bill.
“The logic behind this bill is absolutely preposterous. We could definitely walk away.”
Bonanni branded Mr Johnson’s swipe a “threat” aimed at the bloc, which could lead to “salty” negotiations.
He said: “Basically, Johnson’s words are a threat, while the EU asks Great Britain to pay all the expenses on which it has already agreed, which would reach €60billion.
“Britain says: ‘But we have given some money to the European Investment Bank. Let’s get it back, we are co-owners of EU goods. We want our share back – €25bn.
“The key phrase of Johnson’s speech is the following – he says they can leave the EU…