[3] On 18 June, Željezničar announced the departure of Semir Dacić, Vernes Karavdić and Mirza Šubo.
[9] On 15 July, Željezničar announced the loan of 21-year-old Ivan Milićević from Lokomotiva for the upcoming 2020–21 season.
[14] On 24 August, Željezničar announced six players tested positive for COVID-19, amid its pandemic in Bosnia and Herzegovina.
[18] On 7 September, Željezničar announced that all the players, coaches and club staff tested negative for COVID-19.
[23] On 23 November, Željezničar's chairman of the board Admir Džubur died of complications caused by COVID-19.
[28] On 23 January, Željezničar announced that businessman Samir Cerić had become the new club chairman of the board.
[30] On 30 January, Željezničar announced the loan of 22-year-old Jasmin Čeliković from Rijeka for the remainder of the 2020–21 season.
[31] On 3 February, Željezničar and Mustafa Mujezinović negotiated a one-year contract extension lasting until June 2022.
[32] On 4 February, Željezničar extended their sponsorship agreement with ELPI Comerc and Eko sir Puđa.
[33] On 16 February, Željezničar and Siniša Stevanović negotiated a one-and-a-half-year contract extension lasting until June 2022.