Eichhorn went on to make his big breakthrough in the summer. Leitl invited the teenager into first-team training at the start of pre-season due to a lack of options in the middle of the park, with Paul Seguin, Diego Demme and Pascal Klemens all out injured.
Leitl was not allowed to use Eichhorn in Hertha's friendlies because he was still too young at 15, but had no doubts over his ability. "He's really progressing well, both physically and in terms of his understanding of the game," said the Hertha boss. "He's very eager to learn; we've already had many conversations with him."
Eichhorn also made an immediate impression on his team-mates, with veteran centre-back Toni Leistner telling reporters: "What the lad can do is astonishing. Clear-headed, not at all arrogant. I'm sure Hertha will get a lot of enjoyment out of him."
Hertha were also forced to speed up the drafting of Eichhorn's first professional contract after Eintracht Frankfurt made a play for his signature. The Olympiastadion outfit pulled out all the stops to keep the homegrown ace, who committed to terms through to 2029 on July 4.
"It's absolutely crucial for me that my development in all areas never stops, that's why I see Hertha as the best place for me," Eichhorn declared after signing the deal.
Enamoured by Eichhorn's progress on the training pitch, Leitl included the youngster in his squad for Hertha's first league game of the 2025-26 campaign against Schalke, which they lost 2-1, though he did not make it off the bench. He did, however, come on for the final 22 minutes of their 0-0 draw at home to Karlsruher the following week, in the process becoming the youngest debutant in 2. Bundesliga history at 16 years and 14 days old.
A delighted Leitl said when quizzed on Eichhorn's performance: "I couldn't care less whether he's 16 or 17. He's a huge talent for Hertha. He was in the spotlight today. In many of his actions, you could see what might be in store for us in the coming years. I'm completely convinced by him; he did a good job."