Arsenal defender Kieran Tierney dislocated his shoulder on Monday which could see him ruled out until March 2020, according to Arsenal official website.
Tierney made his fifth Premier League start against West Ham where the Gunners came from a one goal down to win 3-1.
The ex-Celtic defender was forced off the pitch after half an hour when he fell awkwardly on his right shoulder with report suggesting he will be needing surgery and could face a lengthy spell on the sideline.
Tierney who joined Arsenal in the summer from Celtic is reportedly worth around £25m, but has struggled for fitness after he underwent a double sports hernia operation at the end of May 2019.
The 22-year-old will be joined on the sidelines by Granit Xhaka, who suffered a concussion against West Ham as both players are expected to miss Arsenal crucial clash On Thursday against Standard Liege in the Europa League.
The Gunners will also be without a host of player as Nicolas Pepe, Rob Holdings and Hector Bellerin will miss the trip to Belgium due to knee and hamstring injuries respectively
Whist Shkodran Mustafi will miss the game after picking up three bookings at the group stage.