His eighth-placed side host the 11th-placed Robins seeking a first win in six Championship outings.
Taking only five points from the last 24 available means one-time leaders Town have steadily dropped down the table.
Lee Johnson’s Bristol City arrive on the back of a 2-0 home win over Ipswich Town which snapped a sequence of three straight defeats.
They are on 27 points, three behind Town, and Wagner, who suffered two defeats against the West Country side last season, noted: “There is a reason they have that number and they will give us a challenge.
“They are good on offence, have good individual quality and a good idea of how they want to play the game. They are a very interesting side to play against.
“We have to create a plan, put it in he players’ heads and make sure they bring it to the pitch and that our fans can see what the plan is.
“I have no worries over the confidence and self-belief of my players. I think we could see this at Blackburn.
“There is no reason to be less confident, have less trust or less self-belief. Our performances have been too strong for this.
“It’s a case of making right the little details, for example in using some of the many chances we are creating," the German Head Coach added.
“We also need that little bit of luck to win games - but as I said before, you have to work to be a lucky man, and these players are working hard.”
Wagner has right-back Tommy Smith available after a one-match suspension for five bookings.
He has yet to make a final decision on whether to recall him or stick with Martin Cranie, who impressed at Blackburn on his first league start of the season.