The Nigeria striker briefly lost consciousness after hitting his head on the ground after a Cristian Romero challenge in stoppage time of the game in northern Italy.
The 22-year-old was taken to the city's Papa Giovanni XXIII hospital for tests, according to media reports. The forward, who joined the club from Lille last summer, had only returned to action last month after being sidelined for over two months with a shoulder injury and coronavirus. Despite a promising start to the season he has scored just two goals for the club.
Napoli fell to their third defeat in five league games as Atalanta warmed-up for next week's Champions League clash with Real Madrid to move fourth in Serie A.