Ounas was reportedly approached by a group of Frosinone supporters outside the Benito Stirpe stadium, who unsuccessfully attempted to steal his bag.
"Thanks to everyone for your messages, but everything is OK," the 22-year-old wrote on Instagram. "I got my bag back."
The comment was posted as an Instagram story, along with a picture of his recuperated bag and a patch covering his right knee.
Napoli are almost certain to finish the season in second place with Inter eight points behind them in third with four matches remaining.
However, their points total of 70 is 21 fewer than they reached under Maurizio Sarri in the previous campaign, while they suffered disappointing, early exits in the Champions League, Europa League and Coppa Italia.