The Terriers are without a win in their last eight league fixtures, and will enter this weekend's home game against Bournemouth having lost each of their last five top-flight fixtures.
Huddersfield have dropped into 19th position in the table following the poor run, but Wagner is still confident that his side can retain their Premier League status in the final months of the campaign.
"We probably have to over-perform to be successful. We are three points behind the team 12th in the table, after 25 games, and now the crucial time starts for us," Wagner told reporters.
"We all look at the fixtures and we knew we had a difficult spell with the Liverpool and [Manchester] United games. Now we have games against teams, in and around us, and we have a chance and must show our fighting spirit.
"Against the top six it's not impossible, but difficult, to collect points. Now we face teams against whom the chances are a little bit bigger. We now have opponents who are in and around us but we still have to be at our best."
Huddersfield have only scored once in their last six Premier League fixtures.