Maddison was taken off on a stretcher in Sunday’s friendly against Newcastle
Tottenham Hotspurs Football Newsletter
Maddison was withdrawn, just minutes after coming on, with his head in his hands after collapsing to the pitch during a 1-1 draw with Newcastle in South Korea.
He looked distraught and the injury is a major concern for Spurs ahead of the new season, having earlier seen captain Heung-min Son bid farewell to the club before leaving.
Maddison missed the end of last season with a knee injury and now looks set for another spell on the sidelines after damaging the same knee.
Maddison looked distraught as he was taken off
Dejan Kulusevski will miss the start of the season and Spurs missed out on Morgan Gibbs-White, meaning Thomas Frank was already short of creative players.
Frank said: “We're pretty sure it was the same knee he injured before.”
He added: "I think sometimes in life and football things can be both beautiful and brutal. That's what we got today.
“It looks like with Madders a bad injury and then on the other side unbelieveable scenes for Son from his team-mates and the respect from the Newcastle players.”
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Spurs face Paris Saint-Germain in the Super Cup next Wednesday before kicking off the new Premier League season at home to Burnley next Saturday.