Dortmund's 2013-14 UEFA Champions League campaign started poorly on Wednesday with goalkeeper Roman Weidenfeller sent off just before half-time as Gonzalo Higuain and Lorenzo Insigne scored the goals that gave Napoli victory.
The German club had just one less shot on goal than Napoli throughout the match but Zorc said Dortmund were ineffective up front in the first half, which saw them trail 1-0 at the break.
"We had problems, especially in the first half in imposing ourselves on the game," Zorc said on Thursday.
"I think we only managed one good attack in the first 45 minutes.
"I think Robert (Lewandowski) stood alone in front of the goalie during that one. It was a huge chance.
"But apart from that, we didn't manage to develop our offensive game."
Zorc added that Dortmund had moved on from head coach Jurgen Klopp's verbal outburst that saw him sent to the stands at the Stadio San Paolo, while hinting they would accept whatever punishment UEFA decides on for the 46-year-old.
"(Klopp) already admitted to you, the team and most importantly the referees, that he overreacted in that situation and that it wasn't ok. He apologised," Zorc said.
"With that the topic is closed for us.
"We'll have to see what the UEFA wants to do but we can't influence that anyway."
Dortmund headed to Italy having won every competitive fixture of the season prior to Wednesday's game and will need to regroup quickly ahead of a trip to Nuremberg on Saturday.
Nuremberg sit in the relegation zone after five rounds of the Bundesliga, 15 spots below leaders Dortmund, while Zorc's club have won three of their past four games against the Bavarian outfit.
Despite that, Zorc remains adamant Nuremberg will be a tough test.
"The last few years in Nuremberg have never been easy for us although we managed to succeed most times except once... where we drew," Zorc said.
"The challenge will be to bridge the gap from an unsuccessful away game in the Champions League to coming back to the Bundesliga and going into the next game 100 per cent focused to get the points and stay on top of the league.
"That clearly has to be our goal."
