| Nabil Jaadi | a | MAR - BEL | 2017/18 | 1 | 0 | Udinese U19 | | | |
| Anssi Jaakkola | p | FIN | 2009/10 | 1 | -1 | Siena U19 | | | |
| Ali Jaber | d | LBA - TUN | 2024/25 | 1 | 0 | Bologna U19 | | | |
| Darvin Jablonski | d | POL | 2024/25 | 0 | 0 | Hellas Verona U19 | | | |
| Jackson | d | BRA | 2000/01 | 1 | 0 | Vitória U20 | | | |
| Bjarke Jacobsen | c | DAN | 2011/12 | 0 | 0 | Nordsjælland U19 | | | |
| Claude Jacquet | d | FRA | 2025/26 | 0 | 0 | Servette U19 | | | |
| Abderrazzak Jadid | c | MAR | 2000/01 | 1 | 1 | Brescia U19 | | | |
| Jadilson da Silva | c | BRA | 2010/11 | 1 | 0 | Varese U19 | | | |
| Elvic Jager | a | OLA - RDC | 2024/25 | 1 | 0 | PSV Eindhoven U19 | | | |
| Jaime | p | ARG | 1989/90 | 1 | -1 | Newell's Old Boys U19 | | | |
| Jairo | d | BRA | 1997/98 | 1 | 0 | Nacional U19 | | | |
| Matias Jaiteh | d | NOR | 2025/26 | 1 | 0 | Bodø/Glimt U19 | | | |
| Leon Jakirović | d | CRO | 2024/25 | 1 | 0 | Dinamo Zagreb U19, Inter U19 | | | |
| Jordi Jaku | c | ALB | 2025/26 | 1 | 0 | Bologna U19 | | | |
| Edin Jakupi | c | AUT - ALB | 2025/26 | 0 | 0 | Rapid Wien U19 | | | |
| Arnel Jakupović | a | AUT | 2016/17 | 2 | 2 | Empoli U19 |  | | |
| Sulayman Jallow | a | GAM | 2025/26 | 1 | 0 | Fiorentina U19 | | | |
| Antonijo Janjic | d | CRO - GER | 2024/25 | 1 | 0 | Stuttgart U19 | | | |
| Filip Janković | c | SER | 2013/14 | 1 | 0 | Parma U19 | | | |
| Klaidas Janonis | c | LIT | 2014/15 | 0 | 0 | Pro Vercelli U19 | | | |
| Niek Janssen | p | OLA | 2024/25 | 0 | 0 | PSV Eindhoven U19 | | | |
| Daniel Jara | a | PAR - SPA | 2012/13 | 1 | 0 | Genoa U19 | | | |
| Jari | p | BRA | 2000/01 | 1 | -1 | Corinthians AL U20 | | | |
| Nuha Jatta | c | GER - GAM | 2024/25 | 2 | 0 | Torino U19, RB Lipsia U19 | | | |
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