1. FSV Mainz 05 stated on June 3, 2026, that Kasey Bos will join Excelsior Rotterdam on loan for the upcoming season to gather playing experience with the Dutch Eredivisie club. Bos is a 22-year-old Australian left-back who also possesses Dutch citizenship. He had joined Mainz 05 from Melbourne Victory in the previous summer but missed a significant period due to a shoulder injury. Bos has not yet played for the Mainz first team, having made 14 appearances with 4 assists for the reserve team in the Regionalliga Südwest. Niko Bungert, the 05 sporting director, said that it is important for Kasey Bos to get playing time at the highest level and that Excelsior Rotterdam is the ideal club for his development. Bungert also noted that being close to his brother Jordan, who is with Feyenoord Rotterdam, will assist Bos in settling into the new city. His contract with Mainz is valid until June 30, 2029, and his market value, according to Transfermarkt, is €450k.