David Silva was lucky to stay on the pitch after a tackle on Manchester United midfielder Andreas Pereira.
The Manchester City star kicked Pereira in the chest and did not even receive a card.
The challenge came after Leroy Sane doubled Pep Guardiola's side's advantage at Old Trafford.
Sane's shot was not kept out by David de Gea at his near post as he opted to use his feet instead of his hands.
Bernardo Silva gave the champions the lead with a low shot again at De Gea's near post.
The win would take City one point clear at the top of the table ahead of Liverpool.
