Kovač was speaking on the Bild podcast Phrasenmäher and was careful not to enter the transfer speculation surrounding Eichhorn, who is attracting interest from multiple clubs including Manchester City, Bayern Munich and Borussia Dortmund themselves.
"I don't like to talk about players from other clubs. But we have something in common — he is a Hertha player, I was a Hertha player. A great player who has enormous potential and who, like some others, is the future of German football."
Dortmund are understood to be in strong contention for Eichhorn's signature. Eichhorn's release clause sits between €10million and €12million depending on the nature and destination of the transfer. Sky Sport Germany also reported on Monday that Manchester City are planning to trigger the clause and immediately loan Eichhorn to Bayer Leverkusen for a season — a structure facilitated by an existing cooperation agreement between the two clubs.
On the subject of which former teammate he would most like to have in his current squad, Kovač did not hesitate.
"Luka Modrić. I was captain at the time when he came into the national team, and you could immediately see what an extraordinary footballer he is."
Modrić, now 40, is under contract at AC Milan until the end of June and is currently sidelined with injury. Kovač was asked whether a move to Dortmund for his former Croatia captain was realistic.
"It was clear that question would come. But on the one hand, Luka is 40 years old, and on the other he is injured right now. I wish him a quick recovery."
Whether Kovač secures Eichhorn or Modrić this summer, he will have already welcomed Gadou. Dortmund's rebuild under Book is taking shape — and their head coach is not short of ideas about who else should be added to it.