Johnson has already held talks with Brown while former Tigers loan star Mills has been told he is free to leave Eastlands.
Brown said: "Michael and his agent made contact with me over the weekend to say that he would be interested in signing.
"I've had conversations with him in the last few days, but at this moment in time our priorities lie elsewhere.
"Danny has been on the phone as well over the possibility of coming here. We talked about what deal he could take back to Manchester City to get out of his contract there, but as far as I'm concerned it should be a case of him discussing it with his club and then coming to us.
"Danny's wage at Manchester City is quite phenomenal, but rightly so because when he signed it, he was a regular Premiership player," he told the Hull Daily Mail.