The 26-year-old Brazilian came off after 74 minutes after a clash with defender Jan Vertonghen.
Liverpool said a hospital examination confirmed it was an abrasion of the eye, but there will be no lasting damage.
Firmino said in a post on Instagram: "It was just a scare, my eye is ok and so am I.
"Thank you for all the support and see you soon."
Firmino looks likely to play against PSG on Tuesday in what will be Liverpool's opening Champions League group stage match of the season.
Jurgen Klopp also commented on the injury, saying: "I have no clue what exactly happened. But it is something with his eye and, at the moment, it is not comfortable for him."
Firmino scored what would turn out to be the winner in Liverpool's 2-1 win over Tottenham at Wembley.