Liverpool defender Giovanni Leoni is set for a lengthy spell on the sidelines after picking up a suspected anterior cruciate ligament injury during his debut.

The 18-year-old started Tuesday's 2-1 Carabao Cup third-round victory over Southampton and lasted 81 minutes before being forced off.

Leoni, who arrived from Parma in August for 26 million pounds plus add-ons, has since undergone medical tests on his left knee. Early indications suggest the center-back may have sustained ACL damage, an injury likely to rule him out for most, if not all, of the season.

"I want to sincerely thank every single person who has shown me support in this difficult moment," Leoni posted on Instagram. "It wasn't the debut I had always dreamed of, but I will give everything to be back playing in this magical stadium as soon as possible. Thank you so much!"

Manager Arne Slot admitted the player immediately knew the injury was serious. "He is down because, for him, it didn't feel good immediately. Normally the emotions of a player tell you a lot," Slot said after the match.

Leoni's absence leaves Liverpool with just three senior central defenders: Virgil van Dijk, Ibrahima Konate, and Joe Gomez. UEFA rules allow the Reds to replace Leoni in their Champions League squad, with forward Federico Chiesa among the options being considered.