The summer transfer window in football is split into two parts, with the first window opening on Sunday 1 June and the second window opening on Monday 16 June before closing on Monday 1 September at 19:00 BST. This split allows teams participating in the Club World Cup to sign players before the tournament begins on Sunday 15 June. While Manchester City and Chelsea are the two Premier League clubs competing at the Club World Cup, any team can take part in the early window. According to Fifa rules, a transfer window cannot last more than 16 weeks in a calendar year, leading to the split this summer.
Source: BBC
