The Brazilian, who has remained first choice despite the summer arrival of Giorgi Mamardashvili from Valencia, appeared to suffer a hamstring problem and will not feature against Chelsea on Saturday.
Manager Arne Slot admitted after the game that the outlook was not encouraging.
"If my player is on the floor, nine out of ten times I fear the worst and with the worst I mean that he cannot continue," Slot has said. "It's never positive if you go off like this. You can be sure he is not playing Saturday."
Alisson, left out of Carlo Ancelotti's latest Brazil squad for upcoming friendlies against South Korea and Japan, will now await the results of his scan to determine the length of his absence.
Liverpool will hope he can avoid a lengthy lay-off, having already endured hamstring issues in each of the past two seasons. Mamardashvili is set to make his Premier League debut at Stamford Bridge, with summer signing Freddie Woodman expected to provide back-up.
The Reds' injury list has grown in recent days. Forward Hugo Ekitike, who was also withdrawn in the second half against Galatasaray, is being monitored but is hopeful of being available for the trip to London.
The club's record signing Alexander Isak is likely to lead the line regardless, having played less than half an hour in midweek. Mohamed Salah, Alexis Mac Allister and Conor Bradley also came off the bench in Istanbul and are pushing for starts.
Federico Chiesa was absent on Tuesday due to what Slot described as a "little niggle", while teenage defender Giovanni Leoni faces a far longer recovery. The Italian, a twenty-six million pounds summer signing from Parma, tore the anterior cruciate ligament in his left knee on debut against Southampton in the Carabao Cup.
Slot has said the 18-year-old could be sidelined for up to a year.
Leoni confirmed on social media that he has undergone successful surgery, posting from his hospital bed: "Surgery done. Thanks everyone for the messages. I'll be back soon."