Flint - along with left-back Joe Bryan, who has also been linked with a move to Leeds (Bristol Post) - was the subject of an undisclosed bid from Birmingham yesterday (Tuesday), which Johnson confirmed was rejected after being considered 'derisory' by his club.
Aden Flint of Bristol City (right)
And the 36-year-old said he is expecting further approaches for the pair, but added that any sale would be on Bristol City's terms, with the Robins 'in a really good place' regarding the Football League's financial fair play regulations.
That being said, when speaking about Flint specifically, he added: "He's a good lad, Aden - he's definitely had his head turned, there's no question of a doubt about that.
"In the summer we had a conversation with the agent. The agent made it clear that there is interest. And if there is interest where Aden can maximise his earnings and his potential moving forward then they would be interested in exploring it."
"Obviously Aden was really happy to sign his new deal where he was handsomely paid due to the quality of the performances he put in through the years. And this is the catch 22: every player wants to play as high as they can and for as long as they can and we hope that's for Bristol City."
Joe Bryan of Bristol City (right)
Both Birmingham and Leeds are keen to strengthen in Flint and Bryan's positions, with the Blues missing out on John Terry to rivals Aston Villa and holding an interest in his former Chelsea teammate Ashley Cole, while the Whites have lost Kyle Bartley and Charlie Taylor to Swansea City and Burnley respectively.
Flint, who hails from Derbyshire, signed a new three-and-a-half-year deal at Ashton Gate in December 2016.
Will Birmingham City / Leeds United get their man?