The groping occurred Saturday night, Mexican authorities said, according to a report.
Cardinals officials were informed shortly after the incident and sent a flight to return Kugler to Arizona.
He arrived back early Monday morning, the report noted.
Kugler is now the second Cardinals assistant coach this year to face assault allegations.
Former running back coach James Saxon surrendered himself to Indiana authorities in May after he assaulted a woman in her own home.
In October, Saxon was sentenced to a year in jail before having that be suspended in favor of a year of probation.
He resigned from the team that month.
The Cardinals lost to the San Francisco 49ers 38-10 Monday at the Estadio Azteca.