Johnson, who insists that Preston's visit to Ashton Gate is the first of six 'cup finals' for City, said: "We are now into a massive part of the season and the fans will play a big part in that.
"Strong, positive support will only help put the team in a stronger mental state to cope with the pressures that exist at this stage of the campaign.
"I'd ask as many people as possible to come along to support the lads on Saturday in what is another 'cup final' for us.
"The Ashton Gate atmosphere has been rising since the start of the season and has grown into a crescendo as we reach the final stretch. That can only work in our favour and I'd like to thank our loyal fans in anticipation of that support."