MacAnthony previously confirmed that Posh have accepted an approach from Charlton, after denying two unnamed Championship clubs permission to speak to the winger.
But after one Twitter user suggested that Blackburn Rovers might be one of the mystery bidders, the Irishman chose to disclose Birmingham's identity.
Birmingham have made 2 bids which we turned down https://t.co/bgg4j1vjAJ— Darragh MacAnthony (@DMAC102) January 13, 2020
And he added afterwards:
I’ll have no choice if it matches others. Cheers. https://t.co/UekKfvW11r— Darragh MacAnthony (@DMAC102) January 13, 2020
Maddison has buy-out clause - reported to be set at £2.5 million - inserted into his contract.
But with that deal due to expire in the summer transfer window, at which point the 25-year-old will become a free agent, that would be a substantial amount for either Charlton or Birmingham to pay.
Nevertheless, MacAnthony later insisted that whatever the figure, it has indeed been matched.
Earlier this month, MacAnthony admitted that he is planning for life without Maddison at Peterborough.
Middlesbrough and Derby County have also been linked with moves for the player, who has scored or made 128 goals in 212 games in England's third tier.
Charlton, Birmingham or neither - where do you think Maddison will go?
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