Aaron Ramsdale appeared to laugh on the substitutes bench moments after Arsenal's first choice goalkeeper David Raya made a howler against Luton.
Raya, who joined on loan from Brentford last summer, has established himself as Mikel Arteta's preferred choice between the sticks at the Emirates, despite making a handful of significant errors since being given the vote of confidence.
Ramsdale, who played all 38 league matches during Arsenal's title pursuit last season, has since dropped to the bench to make way for the Spaniard.
The goalkeeper's father criticised Arteta's handling of the situation last month, saying 'my son has lost his smile'.