Arsenal captain Laurent Koscielny was taken to hospital after suffering a suspected broken jaw in Friday's 3-1 defeat to Manchester United.
The centre-back was forced to come off in the second half after Manchester United striker Romelu Lukaku appeared to accidentally kick him in the side of the head.
Koscielny, who returned from a seven-month injury lay-off in December, remained down for several minutes with blood visible on his face, before being replaced by Mesut Ozil.
Arsenal head coach Unai Emery, speaking after the FA Cup fourth-round defeat, confirmed Koscielny was taken to hospital for scans.
Earlier in the game, Arsenal lost another centre-back to injury with Sokratis Papastathopoulos having to come off for Shkodran Mustafi in the first half after he appeared to roll his ankle.
Arsenal face a worsening injury crisis in defence, with Hector Bellerin already out for up to nine months after rupturing his anterior cruciate ligament in last weekend's win over Chelsea.