Mustafi suffered the muscle problem while on international duty with Germany during the first half against Azerbaijan as the holders secured their place at the 2018 World Cup on the back of 10 straight qualifying wins in Group C.
Following the 5-1 victory in Kaiserslautern, Germany manager Joachim Loew suggested it was a ‘torn ligament’, which if confirmed would rule the 25-year-old out for a substantial spell.
While Mustafi will be absent when the Gunners resume Premier League action in Saturday’s late kick-off at Vicarage Road, Press Association Sport understands the full extent of the diagnosis is still being assessed .
Whenever the German is available again, Arsenal manager Arsene Wenger has something of a defensive selection poser for the trip to Hertfordshire should he look to continue with a three-man backline.
Germany’s Shkodran Mustafi holds his leg after suffering an injury during the 2018 World Cup qualifyingEurosport
While Spaniard Nacho Monreal is expected to be available, France defender Laurent Koscielny has been nursing a troublesome Achilles which flared up before the international break, while Calum Chambers is recovering from a groin problem.
Rob Holding, who played against Brighton with Koscielny, and v eteran German Per Mertesacker are other options to come in for Mustafi.
Arsenal, though, could be boosted by the return of playmaker Mesut Ozil from his knee injury and also England forward Danny Welbeck, who has now resumed full training after a groin problem sustained during the goalless draw at Chelsea on September 17.
Following two defeats from their opening three Premier League matches, Arsenal are unbeaten through seven outings in all competitions, with four successive victories.