Arsenal defender Gabriel Magalhaes appeared to mock Viktor Gyokeres after scoring on Tuesday night.
The centre-back rose highest to head home Arsenal's third goal in the first-half of their Champions League clash, as the Gunners ran riot in Portugal.
After scoring, Gabriel wheeled away in celebration and interlocked his hands before raising them to his face - identical to the trademark celebration of Gyokeres.
The Brazilian was quickly swarmed by his teammates but users on social media were quick to pick up on the gesture made by the central defender.