Sport Bild reports that Book, who replaced Sebastian Kehl in the role this spring, met Eichhorn directly to outline the club's vision for his development — a step that his predecessor had been reluctant to take, having reportedly harboured reservations about whether signing the teenager could block the progress of Borussia Dortmund's own young midfielders Mussa Kaba and Enzo Duarte. Book's arrival has produced a clear shift in approach.
Eichhorn, born in Bernau bei Berlin in July 2009, became the youngest starter in Zweite Bundesliga history when head coach Stefan Leitl handed him his league debut at 16 years and 14 days in August 2025.
He has since made 15 appearances for Hertha in the second division, playing a little under a thousand minutes in competitive football before being sidelined by an ankle injury in January.
Despite that setback, the interest surrounding him has only intensified. Bayern Munich are exploring a potential swap deal that would see loanee Maurice Krattenmacher go the other way, while Bayer Leverkusen and RB Leipzig have also registered concrete interest. From abroad, Manchester City, Arsenal, Real Madrid and Barcelona are all understood to have had him scouted.
Eichhorn holds a release clause of €10-12 million in his contract — a figure that activates only if Hertha fail to win promotion to the Bundesliga. The club currently sit in a playoff position in the Zweite Bundesliga, making that clause's availability uncertain. A full buyout without the clause would command a significantly higher fee.
Dortmund's pitch centres on the promise of a realistic pathway to Champions League football at a club where established youth talent can earn regular minutes. The argument is one that Eichhorn's camp appears to find persuasive — though Sport Bild noted last week that the player is not yet fully convinced by the Dortmund style of play, suggesting a decision is far from straightforward. Book is understood to be continuing discussions.