Milan mayor Beppe Sala has warned both Inter and the Rossoneri that current proposals for their new stadium will be "impossible" to push through.
The two Milan clubs are eager to leave San Siro, which they believe can't be refurbished to modern standards.
They presented their plans at the end of September and while they received approval from the municipal council last week, it was only conditional.
Speaking at a military ceremony on Monday, Sala was asked for an update on the situation.
"We must get to work with the teams to understand how we can reach an agreement between their needs and ours.
"It is obvious to everyone that the volume [of land] requested is impossible. It is excessive.
"However. from this point of view, we want to try and find a solution with the clubs."
In the meantime, Serie A wants to propose San Siro as a UNESCO world heritage site - something that the politician rejects.
"Such a proposal does not help because now we are at the stage of technical discussions [over a new stadium].
"I believe the city is not rejecting a new stadium out of hand, but it is neccessary to find the right solutions from a financial point of view and in terms of what will be built."
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