With Manchester United also keen, Milan have made a first move for the Ecuador international.
Sky Italia says Milan's bid has been rejected by Brighton.
While the offer hasn't been revealed, it's understood there is room for Milan to make an improved proposal.
The Ecuadorian's contract with Brighton runs until the summer of 2027.
Brighton are said to be seeking £40m to sell Estupinan, with a first United bid soon expected.
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Manchester United
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William379
0
If it was Chelsea asking, they would want £100m
suoadkltuz
1
Estupinan is for Brighton , why mentioning Man U you morons .
man united target
yewadklnrs
0
the guy is a very good defender
yewadklnrs
0
the guy is a good defender
vitinha23
0
Please Manchester United don't dive in wait for a moment let's monitor the situation and see how much the need before making move!
Tiyabmnops
0
Estupinan is for Brighton , why mentioning Man U you morons .