Frank says the issue has hurt their season.
"It is of course serious - we have had far too many injuries," said the Dane.
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"We are doing a big review of what kind of injuries we have had and how quickly the injured players have returned to being able to play.
"This is what we are investigating across all departments. This applies to the coaching staff, sports science, the performance department and the medical department. Everything is connected.
"The main reason is that we have been very unlucky. There have been a lot of contact injuries and a lot of big injuries like cruciate ligaments that are difficult to do anything about.
"But we are still investigating what we can do to improve it all and how we can avoid it."