Arsenal boss Arsene Wenger revealed that star man Laurent Koscielny picked up an injury during the 3-2 Champions League defeat to Olympiakos, according to reports from the Express.
The 30-year-old was forced to come off after he was believed to have injured his right leg following a sliding tackle in the recent match.
Per Mertesacker was eventually brought on to replace him with Wenger later confirming during the post-match press conference that the France international was hit with a hamstring injury.
His latest knock will be seen as a huge blow to the Gunners given that they host Premier League leaders Manchester United at the weekend.
Koscielny is now expected to join a long list of unavailable stars on the sidelines, with Mikel Arteta, Mathieu Flamini, Jack Wilshere, and Danny Welbeck all out.
Petr Cech is also a doubt for the upcoming clash against United with a calf injury and was rested for the European tie yesterday as David Ospina was called upon to take his place between the sticks.