Raheem Sterling took a blow from veteran Porto defender Pepe's knee during a feisty Champions League encounter at the Etihad on Wednesday night.
The visitors took the lead early on through a brilliant individual goal by Luis Diaz, but a Sergio Aguero penalty soon after and goals from Ilkay Gundogan and Ferran Torres after the break secured a 3-1 victory for Pep Guardiola's side.
But it was deep in the second-half where Pepe's frustrations boiled over after Sterling went down softly looking for a penalty, as the 37-year-old screamed at the England international before dragging his knee into the side of Sterling.