The highly-rated 22-year-old has attracted interest from a number of European clubs, with Serie A sides Roma and Chievo, alongside City, reported to be keen on his services.
City have strong relations with the Norwegian side as they currently have three players - Abdisalam Ibrahim, Bismark Boateng and Razak Nuhu - out on loan there, but Flo dismissed a move in the opposite direction for Johansen.
"Manchester City might keep tabs on him," he told Drammens Tidende.
"They probably think that he is a good footballer, but there is no plan for City to buy him or loan him back to us.
"There are two or three European clubs who are seriously interested in Stefan.
"I am expecting that something will happen before Christmas. I am expecting that they will show their interest, but I am not certain.
"Stefan will most probably not stay with us until his contract expires. We are in regular contact with his agent."