Last season's Bundesliga runners-up, who open their campaign against Bayer Leverkusen on Saturday, will be without Kirch for at least eight weeks with a thigh muscle injury, it said in a statement.
His South Korean team mate, who joined from Augsburg this season, will be out for an estimated four weeks with a thigh muscle tear.
Both players were injured in training on Tuesday afternoon and underwent checks in a Dortmund hospital on Wednesday that confirmed their injuries.
Dortmund are also competing in the group stage of the Champions League, starting in September.
- Sports & Recreation
- Disease & Medical Conditions
- Bayer Leverkusen