Stefan Klos says Rangers can't rest on their Europa League laurels just yet.
But the former Ibrox and Dortmund keeper reckons the Scottish champions have nothing to fear in a "Jekyll and Hyde" Borussia team.
Gio van Bronckhorst's side tore Dortmund apart at the Westfalenstadion and return to Glasgow next week with a 4-2 lead to defend.
Raphael Guerreiro's strike in Germany may have kept the tie alive, especially if Dortmund can count on the return of free-scoring Erling Haaland for their trip to Ibrox.
But Klos, who was amazed by what he saw in the first leg, believes Rangers have "nothing to fear" so long as they show the same bravery they did on Thursday night.
Even if Dortmund bring their A-game in their bid to reach the Europa League round of 16.
He said in the Sunday Post : “For a Scottish team to play so boldly against Dortmund was very, very refreshing and probably a little bit unexpected. Overall, it was very powerful and impressive. Dortmund must have been taken by surprise by the tactics.
“Rangers were just very comfortable for long spells in the game. At times it looked as though Rangers had a man extra on the pitch.
“When Dortmund tried to press Rangers, Rangers always found solutions. Their movement off the ball is excellent. It was a very mature performance.
“But the fact Dortmund got that second goal to make it 4-2 means the tie is still very much alive.
“However, for all the quality Dortmund possess, I don’t think Rangers have anything to fear. They should feel comfortable without being over-confident.
“The reputation of Dortmund in Germany is that they are a Jekyll and Hyde team. Nobody is sure which one will turn up.
“It is impossible to predict how they will play.
“But even if they do bring their best game to Ibrox, Rangers can still do it. They are in a really strong position."