Kacper Kostorz has joined Polonia Warszawa on a free transfer after his contract with Pogoń Szczecin was terminated by mutual agreement. Polonia Warszawa confirmed the signing and announced that a contract is valid until June 30, 2029. After signing the contract, Kacper Kostorz expressed that he was excited to join the club and stated that he wants to help the team achieve promotion.

Kacper Kostorz, a 26-year-old Polish centre-forward, became a free agent by resolving his contract with Pogoń Szczecin. The impending termination was first mentioned by Pogoń's owner, Alex Haditaghi, in a conversation with Goal.pl. As a free agent, Kostorz attracted interest from other clubs, and Piotr Janas of „Gazety Wrocławskiej” reported that Śląsk Wrocław was a potential suitor. According to information from Kamil Bętkowski of Meczyki.pl, Kostorz will join the first division side Polonia Warszawa, and the transfer is expected to be finalized soon. His current Transfermarkt market value is €300k and he has two caps for the Poland U20 national team.