Napoli are concerned after Lorenzo Insigne crumpled to the ground when taking a corner kick, limping off against Juventus.
The Partenopei captain stepped up to take the corner when it was 1-1 at the Stadio Diego Armando Maradona.
He scuffed it and immediately fell down in agony clutching the area above his right knee.
Insigne was able to get back on his feet and limp off, but was spotted grimacing on the bench.
The Italy international was strapped up and it remains to be seen if the problem is his knee or the muscle just above it.
There are now understandably worries ahead of the opening Europa League game against Leicester City, which is scheduled for Thursday.
This was meant to be a happy occasion for Insigne, as against Juventus represented his 400th competitive appearance in the Napoli jersey.
He is only the fourth player to achieve that with this club, after Antonio Juliano (505), Giuseppe Bruscolotti (511) and Marek Hamsik (520).
Si fa male #Insigne! Sugli sviluppi di un calcio d’angolo dalla destra, ha sentito un dolore al ginocchio destro dopo aver calciato. Esce dal terreno di gioco e al suo posto entra #Zielinski. Per il capitano subito una vistosa fasciatura e la borsa del ghiaccio.#NapoliJuve pic.twitter.com/BaFuIIbULN
— Simone Guadagno (@SimoneGuadagnoo) September 11, 2021