It seems Dortmund is not sure about hiring Serhou Guirassy anymore. Serhou Guirassy had an amazing performance during last season in Stuttgart and he was an effective player for this team. This made Dortmund think about hiring this player. But in the medical tests before signing the contract, the situation of Guirassy was not good enough and that's why there is going to be a delay.
Dortmund is ready to pay 18 million euros for Guirassy.

I think this delay is only temporary and in the end Dortmund will still bring in Guirassy as a mainstay player in the coming season to try to catch up with Leverkusen and Bayern Munich.
In my opinion, Guirassy's injury is not too serious and will not affect his performance and Dortmund have also accepted all the risks after accepting Guirassy's arrival.
At first I was a little surprised by the news of this postponement but after I thought again if he still had a big chance to join Dortmund who currently has a big goal of appearing stronger to compete for the title and only with Guirassy, Dortmund could have a big chance to get closer with the Bundesliga title.