The Championship side could reach their first major cup final in over a century if they manage to overturn a 2-1 deficit in the second leg of the Caraboa Cup semi-final at Ashton Gate.
Johnson said : "For me, and the club, the Premier League is the dream. But saying that, as far as this team is concerned, for this team to beat Man City and the players they have got, it would rank as one of the best results in the clubs history.
They will go down in folklore. Some already have from the Manchester United game. We're going to enjoy it".
Their League Cup semi-final appearance is also their first since the 1988-89 season, where they lost over two legs to Brian Clough's Nottingham Forest.