Television footage shows Herrera spitting on the large badge on the floor at the entrance to the tunnel at the end of the first half.
United were 2-0 down a the time but came back to win 3-2.
It is understood City officials feel it was deliberate and have not ruled out a complaint to the Football Association.
But a United spokesperson said Herrera did not see the City crest as he was making his way off the pitch.
“Ander has seen footage of the incident and is mortified at any suggestion his actions were deliberate.
“It was entirely accidental and there was no intent whatsoever.”