Union Saint-Gilloise has a definite interest in Mateo Biondic, a striker from Eintracht Trier. According to Fabrizio Romano and several Belgian and German sources, both clubs have reached an agreement regarding the transfer. A medical examination for Biondic will take place soon, and if he passes it successfully, the transfer to the leader of the Jupiler Pro League will be finalized. Biondic will not be eligible for the Champions League group stage but can be registered for a potential intermediate round.

Fabrizio Romano reports that Belgian champion Royale Union Saint-Gilloise has signed Mateo Biondić, a 22-year-old forward of Croatian descent. Biondić, who was born in Germany and holds both German and Croatian citizenship, is moving from a semi-professional league to a club competing in the Champions League. He joins from Eintracht Trier, whom he joined in July 2025, in the fourth-tier Regionalliga Südwest, where he scored seven goals and provided five assists in 17 appearances this season. According to Transfermarkt, he can play as a central forward, wing forward, or attacking midfielder. His current Transfermarkt market value is €100k.