Rhian Brewster will be assessed in hospital after being carried off on a stretcher during Friday evening's under-23 game against Manchester City.
The 17-year-old sustained the injury when he landed awkwardly after challenging for a header in first-half stoppage time, the Merseyside club said.
Liverpool Under-23s manager Neil Critchley told the club's website after the 3-2 defeat: "It's not looking good. He fell awkwardly and it's down towards the bottom near his ankle.
"He will be going to hospital. I don't want to speculate too much but he's in a lot of pain and hopefully it's not as bad as it looks, but we fear the worst a little bit at the moment.''
Brewster, who won the Golden Boot in England's Under-17 World Cup success in October, has yet to make his senior debut for the Reds.