Pep Guardiola warned his Manchester City players of the standards he expects when they are on the bench.
The Blues boss was captured by the TV cameras on Tuesday night during the Champions League game with Atalanta venting his anger as John Stones took his time to replace the injured Rodri.
While some have since tried to downplay the incident, Guardiola made no attempt to hide his displeasure when asked about it ahead of their game against Aston Villa and reminded that they always have to be ready to go on.
"Did you see the image? It speaks for itself," he said.
"The guys on the bench know you have to be ready to go out from the first minute. Sometimes it's the t-shirt or other issues."
Guardiola is hopeful that Stones can prove his fitness and build his form as the squad continues to struggle with injuries. Nicolas Otamendi missed the game at Crystal Palace with a problem, and makeshift centre-back Rodri is now out until after the international break.
Aymeric Laporte has been a major miss, having suffered cruciate ligament damage against Brighton in August. City's boss has been told that the rehabilitation is going well but did not have a specific date for his return.
"They told me five or six months so January or February more or less. I don't know. I have the information that it is going well but I don't know."