Kamil Kościelny, a 34-year-old Polish national, has rejoined Stal Mielec, the club where he is a youth product, which is his second return to the team. The experienced central defender is the first-division club's first signing of the 2026 summer transfer window. The move was a free transfer after Kościelny's contract with his former employer, Miedź Legnica, expired. He has signed a contract with Stal Mielec that is valid until June 30, 2027. According to Transfermarkt, his current market value is €50k. During the 2025/2026 season, he made a combined 27 domestic league appearances for Miedź Legnica, scoring 4 goals and providing 3 assists.