Arsenal midfielder Aaron Ramsey picked up a calf strain during the 2-1 defeat against Watford at home on Tuesday and came off the ground after 20 minutes.
With Santi Cazorla, Granit Xhaka and Mohamed El Neny all unavailable and Jack Wilshere on loan to Bournemouth, Arsenal now face a midfielder shortage ahead of their weekend clash with Chelsea.
Commenting on Ramsey, Wenger said: “He has a calf strain. We don’t know how long he’ll be out for yet.”
Alex Oxlade Chamberlain, Alex Iwobi or Ainsley Maitland Niles could be given the role at the centre of the park in absence of Ramsey.