The Danes have pledged to introduce stricter measures to ensure there is no spread among the rest of his team-mates as the 19-year-old enters isolation.
However, they don’t think it was picked up within the club and the remainder of the squad has tested negative ahead of the weekend’s match with Odense.
Celtic have had their own covid disruption this pre-season too, with winger James Forrest unable to take part in the club’s pre-season camp in Wales after being identified as a close contact of a positive case and forced into isolation for ten days.
Midtjylland, who face Ange Postecoglou’s side at Parkhead on Tuesday, explained: “Aral Simsir has been tested positive for Corona and is in isolation. He is presumed to have been infected privately and thus not in the club's environment. He has not shown any symptoms.
“Players and staff will make the necessary reservations, and we have launched stricter measures.
“The rest of the team has tested negative and will be tested again before Friday's match against OB in the 3F Superliga. Thus, everyone who is on or around the team will have repeated negative tests before participating in combat.”
Celtic will prepare for the game with a home friendly against Preston North End on Saturday and could have a new signing within their ranks. Talks are ongoing and deals believed to be close for defender Carl Starfelt and winger Liel Abada.