Arne Engels joined Celtic from Augsburg in 2024. Celtic had previously rejected a multi-million pound offer from Nottingham Forest for the 22-year-old in the winter transfer window. Engels had been keen to move to English football. West Ham wanted him to be available for the opening day of the season, which complicated the timing of his potential departure.
The injury to Canada right-back Alistair Johnston, who will be out for a few weeks, has likely contributed to Engels' decision to leave Celtic for West Ham. Johnston had attracted interest from Everton before suffering a leg muscle injury. Celtic have recently signed Egypt winger Haissem Hassan and Germany Under-21 midfielder Mika Baur.