The Mirror says Blues manager Roberto Martinez wants to pay his previous employers just £12m plus extras for McCarthy, who he signed and brought through the ranks.
But Latics want £15m, in a deal potentially rising in value to £20m.
Wigan need to ask for such a big fee as Martinez agreed to pass a whacking 20 per cent of the profit from his sale to Hamilton Academical, the Scottish club he bought the Glasgow-born Ireland international from four years ago.
Hamilton have already received £3m from Wigan for the 22-year-old, and would be due a further £2m-plus from McCarthy's departure.
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