The English winger is alleged to have travelled back to England early during lockdown without the permission of his club, while there were also pictures posted online of the star having a haircut with teammates without using a face mask during the coronavirus pandemic.
Barber Winnie Nana Karkari told Blind: "I only removed the mask for the photo, otherwise all hygiene measures were followed exactly.
"I disinfected every machine in front of every customer, always cut with gloves regardless of Corona - and I am very, very picky."
Zorc has now commented on the claims.
He told reporters: "To our knowledge Jadon has been in Dortmund for weeks.
"I even read that we have put him into a two-week long quarantine and faked an injury. I can only say that is completely wrong.
"Jadon has had a calf injury for weeks, which is why he could not participate in training."
He also addressed the haircut, and revealed he had talked to his player over the incident.
He added: "We have spoken to both the hairdresser and the player. Both have ensured us that the measures of hygiene have been respected at all times.
"They even wore a protection shield and gloves, which were only taken off for the picture. Obviously this is not right. We have made that clear once again to the players.
"In this special situation that we are all in due to Covid-19 it is not just the duty of the coaches to keep an eye on discipline. The whole club needs to do that, this includes the board.
"We have spoken to the players in the past. Also with Jadon. We must not forget Jadon is still a very young player, testing his boundaries.
"I don't think I'm accused of protecting him all the time, as I have sanctioned him when there have been misconducts from his side."