Dortmund are in danger of missing out on Champions League qualification from the Bundesliga and it has been suggested that could result in Haaland moving on.
The 20-year-old has scored 51 goals and supplied 11 assists in 55 appearances in all competitions since arriving at Dortmund from Salzburg in January 2020.
Those goalscoring exploits have seen him linked with a host of major European clubs, including Real Madrid, Barcelona, Manchester City, Manchester United and Paris Saint-Germain to name but a few.
He was unable to find the back of the net in Wednesday's 2-0 victory over Union Berlin, with Marco Reus opening the scoring on the rebound after the Norway international had a first-half penalty saved.
Dortmund remain four points adrift of fourth-placed Eintracht Frankfurt with four Bundesliga games remaining, but Zorc is confident of holding onto Haaland even if they miss out on a place in next season's Champions League.
"We have made our position clear on the Haaland case," Zorc told Sky Sport.
"The decision will not be made without Borussia Dortmund. No matter where we end up, Erling will continue to play for us."
Raphael Guerreiro wrapped up the win for Dortmund late on against Union, but a booking for Mats Hummels ruled him out of the crunch weekend meeting with third-placed Wolfsburg.
After an incredible 2019-20 season during which he scored 20 goals and provided 19 assists in 44 games, Sancho has battled to begin this campaign.
In 12 games, the England international has netted three times and provided four assists, and he is yet to open his account in the Bundesliga.
Speaking ahead of Dortmund's trip to Eintracht Frankfurt on Saturday, Zorc backed the attacker.
"I believe it is easy to see that he is not in the best of form," he told a news conference.
"I can tell he tries hard when he's subbed onto the pitch. He tries to force the lightness and fluidity that he has onto himself.
"Jadon is a player who doesn't talk a lot but who delivers answers on the pitch. Whether this is tomorrow, in a week or at some other point, I don't know.
"What I do know is that it will happen."
Still linked with a move to Manchester United, Sancho is being presented with fewer chances at Dortmund.
His big chance total per 90 minutes in the Bundesliga this season is 0.33 – the lowest since his debut in Germany's top flight in 2017.
However, Sancho is having more shots (2.15 per 90 minutes) and shots from inside the box (1.49) than in any other season.
His 38.78 successful passes in the opposition half per 90 minutes is also his highest, as are his 64.14 passes, but his chances created are well down at 1.82. He managed 2.71 per 90 last season.
With Erling Haaland sidelined due to a hamstring injury, Dortmund – who are fourth in the Bundesliga table – will be hoping Sancho can recapture his goalscoring form to finish 2020.
