Napoli forward Victor Osimhen underwent tests in hospital on Sunday after being carried off on a stretcher following a blow to the head in the team's 4-2 Serie A loss to Atalanta.
Osimhen collided with Atalanta's Cristian Romero and fell to the ground in the closing moments of the game, with reports in Italy saying he then lost consciousness on the pitch.
Former Lille star and Nigeria international Osimhen was taken away by ambulance and was due to spend the night in a Bergamo hospital.
Napoli said only the 22-year-old had suffered "head trauma" that necessitated tests to determine whether there was any damage.
In a statement, Napoli said: "The player will remain in Bergamo until tomorrow [Monday] under the clinical observation of the [Napoli] health manager Raffaele Canonico."
Osimhen became Napoli's record signing when he arrived from Ligue 1 outfit Lille last July, joining in a €70million deal.