Laurent Koscielny has suffered what appears to be a hamstring injury during Arsenal's meeting with Bayern Munich, forcing him to leave the field.
The change came after 49 minutes, with Gabriel Paulista coming on to replace the France international defender.
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And the enforced change did not seem to help matters for the Gunners, with Bayern scoring two without reply inside the 10 minutes after the centre-back was forced off.
The north Londoners have been knocked out at the last 16 stage by the German giants in two of the last four seasons and already appear to be on their way out once again.
Arsene Wenger's side had been level going in at half-time, with Alexis Sanchez cancelling out Arjen Robben's stunning opener.
But Koscielny's withdrawal saw a collapse at the back, with the Gunners undoubtedly hoping that the Frenchman's injury isn't too serious and that he'll be in contention for the second leg.