According to Alex Richards of the Mirror, a statement from Arsenal explained the club are in discussions with the police following an attempted car-jacking in July. The Gunners said further investigations are ongoing.
"Mesut Ozil and Sead Kolasinac will not be part of the squad for our opening match against Newcastle United following further security incidents which are being investigated by the police.
"The welfare of our players and their families is always a top priority and we have taken this decision following discussion with the players and their representatives.
"We are liaising with the police and are providing the players and their families with ongoing support.
"We look forward to welcoming the players back to the squad as son as possible.
"We will not be making any further comment on the matter."
Ozil's car was attacked by a gang wielding a knife in north London, leading Kolasinac to confront the attackers before escaping the attempted robbery.
Goal shared footage on Twitter of the original incident:
Both players would have been expected to be part of Unai Emery's matchday squad against Newcastle, and the Gunners will hope the matter is resolved as soon as possible.