The January transfer window is one of the most entertaining parts of the season for football fans as clubs sign new players and supporters get excited to see what these new arrivals can add.
Similarly, in FIFA 21 the January transfer window also opens up new possibilities for teams in Online Seasons and FIFA Ultimate Team.
People also often wait until after the transfer window closes (this season it will happen on February 1) to begin new challenges in Career Mode so that all the teams have their new squads for the rest of the season.