Johnson, however, has refused to be drawn on the report that he is unimpressed with the youngster: "I would like to say something, but I can't," he has told the club's official website.
"Things will come out when they need to.
"People will be informed in the next few days."
Blackman has made just two first team appearance's for City since joining the club, both in the Carling Cup 1st and 2nd Round ties.