Mainz 05 striker Andre Schuerrle returned to training late this week following a broken toe but it is still unclear whether he will be fit to play against Cologne on Sunday, the club said.
Schuerrle has been key to his team's spectacular run this season, scoring 10 goals and setting up another three.
Former Eintracht Frankfurt captain Ioannis Amanatidis has been ruled out of Saturday's game against second-placed Bayer Leverkusen after coach Michael Skibbe said the midfielder was not part of his immediate plans.
"Michael Zorc is leading our transfer policies and he has proven that this job is in safe hands," said Dortmund CEO Hans-Joachim Watzke.
Zorc has been credited with several successful signings, including Shinji Kagawa, who came from Japan's second division for 350,000 euros but has impressed in his first season before being injured in the Asian Cup last month.
