The Barcelona midfielder believes Athletic Bilbao should have been down to 10 men before Iker Muniain's goal ended the Blaugrana's unbeaten start to the Liga season
The 24-year-old bundled over Neymar shortly before the game's only goal, only to receive a yellow card, despite appearing to be the last man.
And Busquets feels that a red card for the Basque outfit would have changed the outcome of the match.
"I think it would have changed the game," he told reporters when asked about the incident.
"He was bearing down on the goalkeeper. I don't know where [Athletic defender Mikel] Balenziaga was, but it was a clear one-on-one. To me it's a red card. The referee did not do his job well.
"We must continue on this line because we know it's going to be difficult."
Barca were on top for much of the first half and appeared to dip in the second half and Busquets has called upon his team-mates to learn from their mistakes.
He added: "In the second half, they pushed better. We're not a team who can be like Athletic, at a high intensity, but we have our own strengths. We should not get alarmed.
"We have to carry on, win the remaining games this year and learn from the mistakes the positives."