Striker Gerard Moreno gave Espanyol the lead after 66 minutes, but Gerard Pique levelled for Barcelona in a tensely-fought clash at the Cornella-El Prat stadium.
According to Sport, Barca sources told the website that Umtiti was called a "black shit" by Espanyol striker Sergio Garcia following the game.
The two players, who allegedly began to argue after the final whistle, had to be separated in the tunnel.
The website also says that referee Jesus Gil Manzano noted the incidents, but not the specific details of the exchange between the two.
The result, which maintained Barcelona's unbeaten start to the season, took the club nine points clear of nearest rivals Atletico Madrid in La Liga.