Isak scored the opening goal in Liverpool's win in the capital but was immediately forced off the pitch after a heavy challenge from Spurs defender Micky van de Ven inside the penalty area.
Sources told ESPN the forward is thought to have injured his lower leg, with an MRI scan required to determine the severity of the problem.
Should Isak be sidelined for a significant period, it would be a major blow for a player who has struggled for both form and fitness since his £125 million ($166.18m) summer move from Newcastle United. His strike against Spurs was just his second for Arne Slot's side in the Premier League and followed a smart pass from fellow summer signing Florian Wirtz.
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Isak's absence would also pose problems for Slot as he tries to navigate the festive period with a dwindling squad. Forward Cody Gakpo is currently sidelined with a muscle problem while Mohamed Salah is representing Egypt at the Africa Cup of Nations.
Speaking about Isak's injury on Saturday, Slot said: "I don't have any news on him but if a player scored and then gets injured and doesn't try to come back on the pitch, that's usually not a good thing but I cannot say anything more than that.
"It's just a gut feeling but nothing medical to say about it. I haven't spoken to him yet.
"It's a good thing that he scored. A good goal assisted by Florian Wirtz."
