The Terriers have suffered heavy defeats to Chelsea and Manchester City, but Wagner's side are favourites to prevail against newly-promoted Cardiff at the John Smith's Stadium.
However, Wagner has been full of praise for the Welsh side, with Neil Warnock helping the Bluebirds to promotion against the odds last season.
At a press conference, the German told reporters: "We are aware of how Cardiff City will play; very physical and direct but they have a lot of quality in the final third. It'll be a tough test and we have to be on our best.
"Cardiff City are very good in their style, big credit to Neil for what he's done."
The two clubs both sit in the bottom five of the top-flight standings.