Kolasinac has been on international duty with Bosnia over the past week and played 90 minutes against the Netherlands on Sunday.
The 27-year-old trained with his Bosnia team-mates on Tuesday night ahead of their Nations League match with Italy on Wednesday.
Kolasinac, however, was tested for the virus again on Wednesday morning and his result for Covid-19 was positive.
The defender will now miss Bosnia’s game with Italy on Wednesday and Arsenal’s trip to Leeds United on Sunday. He is also a major doubt for the Gunners’ Europa League clash with Molde a week on Thursday.
“It is about Sead Kolašinac who was retested this morning.
“The results of that test have just arrived, which show that our defender is positive for the SARS-Cov-2 virus.”
Kolasinac becomes the latest Arsenal player to test positive for Covid-19 during the current international, with Mohamed Elneny doing so while with Egypt.