Origi was withdrawn before half-time against Newcastle at the weekend as Liverpool continued their 100 per cent winning start to the Premier League season with a 3-1 victory.
Reds manager Jurgen Klopp said on Saturday Origi would undergo a scan and was hopeful the issue was "not that serious", but the Belgian striker was absent from the 20-man group that travelled to Naples on Monday afternoon.
Teenager Rhian Brewster has taken Origi's place in the squad as Liverpool begin the defence of their European crown against a side that have finished Serie A runners-up in three of the last four seasons.
Fellow forward Sadio Mane and full-back Andy Robertson have been cleared, as expected, after Klopp confirmed the pair suffered minor knocks at the weekend.
Midfielder Naby Keita and goalkeeper Alisson Becker remain sidelined but Klopp said last week he is hopeful the former will start training soon, having not featured since the Community Shield because of a hip/groin concern.
Meanwhile, Klopp played down suggestions Liverpool's Champions League triumph last season makes them the best team in Europe.
The Reds made up for missing out on the Premier League title by one point to Manchester City by clinching the most coveted prize in European club football by beating Tottenham in the Madrid final in June.
Klopp, though, insists Liverpool cannot dwell on their success as they prepare to begin the defence of their crown against Napoli in their Group E opener.
He said: "We cannot be the best team in Europe because Man City is the best team in the world, that's the same planet, I heard! There are a lot of good teams out there and you have to prove that constantly."