The defender is on trial with the SPL outfit during their pre-season Austrian training camp and is set to play in Saturday's friendly against 1860 Munich.
"We have been impressed with him so far and we have been encouraged to explore what it will take to bring him to our club," McGhee told the Press and Journal.
"I have received an e-mail from his agent so dialogue has started, but we will not push the button on anything until after we have seen him in action.
"I am still trying to establish whether or not we can get permission to play the other players so we will have to wait and see."
Johnson is keen to move to Scotland after suffering relegation to the French third division last season with Amiens.
He said: "I am on trial to make sure I have a contract at the end of the trial.