The German centre-back picked up an injury in a pre-season friendly against Lens last Friday and could be out until December with serious damage to his knee ligament.
According to Mirror Football, that has forced Arsene Wenger to accelerate his efforts to acquire defensive additions, with Shkodran Mustafi and Fabian Schar on his transfer hit list.
The latter defender represented Switzerland alongside Gunners signing Granit Xhaka at Euro 2016 and largely impressed, as part of a backline that conceded just three goals at the tournament.
The 24-year-old currently plies his trade with Hoffenheim, signing for the Bundesliga outfit last summer after lifting three consecutive Super League titles with FC Basel.
Accordingly, it seems unlikely the 21-cap centre-half will be available on the cheap this summer, with his contract not due to expire for another three years.