The Swiss midfielder has promised that the Partenopei will bounce back at Signal Iduna Park, after slipping to a surprise domestic defeat to Parma.
The midfielder was speaking after Saturday's shock 1-0 defeat to Parma at the San Paolo, a result that condemned the Partenopei to back-to-back Serie A defeats for the first time in almost a year.
The Swiss international acknowledged changes need to be made, but he is still confident they can stop the rot when they visit Signal Iduna Park.
“After the defeat against Juventus we were hoping to redeem ourselves, but instead we’ve suffered an unexpected defeat,” Inler told reporters. “Parma have closed down well in all areas but we have to be more ruthless. We weren’t able to open the game up and so Parma has had an easy time of it.
“It will be a completely different game and a whole other Napoli [in Dortmund]. We have to make sure we get back to our best.”
Dortmund's preparation for the crunch European fixture hasn't gone to plan either, with last year’s beaten finalists routed 3-0 by rivals Bayern Munich on Saturday.