Liverpool defender Giovanni Leoni faces months out with a torn cruciate ligament in his left knee, according to Sky in Italy.
The centre-back suffered the injury making his Liverpool debut in last night's Carabao Cup win over Southampton.
Leoni was stretchered off in the 78th minute with his left knee strapped up, having impressed on his first appearance since signing from Parma in the summer for £26m.
Head coach Arne Slot said at full-time that the 18-year-old was "down, because for him it didn't feel good immediately".
"This is something now we have to assess and normally these things don't happen in five to 10 minutes, you have to wait until tomorrow to see how he comes in and then maybe do an MRI scan to know more," Slot said.
"Let's hope for the best."
The news is a blow to Slot who only has Virgil van Dijk, Ibrahima Konate and Joe Gomez as alternative recognised centre-backs.
Leoni has pledged to return as soon as possible. "I want to sincerely thank every single person who has shown me support in this difficult moment," he wrote 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!"
Does Slot now have a problem in defence?
Sky Sports' Zinny Boswell:
"Liverpool were already a defender light after Palace pulled the plug on their deal to sign Marc Guehi on deadline day and the reaction from Leoni as he came off in the 81st minute suggested he was in some pain and it could turn out to be an issue for Slot.
"With Leoni out for an extended period it leaves Gomez as the only senior option to back up starting centre-back pairing Van Dijk and Konate.
"Liverpool academy graduate Rhys Williams, who was on loan at League Two Morecambe in Slot's first season, was an unused substitute on the bench against Southampton and could be another option at centre-back."
