Arsenal fear Francis Coquelin could face a lengthy spell out after damaging his knee ligaments in the defeat at West Brom.
Coquelin had to be substituted in the first half of the 2-1 defeat following a challenge on Baggies midfielder Claudio Yacob.
At present the severity of the injury remains unclear, although the Frenchman left the Hawthorns on crutches and has already been ruled out of Tuesday’s crucial Champions League clash with Dinamo Zagreb.
The 24-year-old has emerged as a key member of Arsenal’s starting XI after starring in the 2-0 victory at Manchester City last season, sitting in front of the back four to shield the defence.
Should Coquelin be ruled out for a lengthy period of time then Arsene Wenger’s decision not to sign any outfield reinforcements over the summer will come under further scrutiny.
Mikel Arteta, who replaced Coquelin at the Hawthorns, also had to be replaced after picking up an injury, and will miss the visit of Dinamo Zagreb too.
Wenger’s midfield options are now severely depleted with Jack Wilshere, Danny Welbeck, Tomas Rosicky, Theo Walcott, Aaron Ramsey and Alex Oxlade-Chamberlain all miss the trip to West Brom.