Johnson told BBC Radio Bristol: "Talks have been ongoing and hopefully he's happy with what's been put forward.
"I'm leaving that to the powers that be but I'm sure that he'll be a City player for longer than this season.
"We've always seen him as a major part of our squad. And he's certainly come up trumps and been a major player in our last 10 to 12 games with his goals, work-rate and presence.
"He's getting back to that unplayable Dele Adebola that we know he is."