Nicola Pearson, BBC Sport
The playmaker, signed from Leicester City for £40m in the summer, has been winning plaudits aplenty for his standout performances during Spurs' impressive start to the season.
Maddison has slotted seamlessly into Ange Postecoglou's high-intensity style of play that - before their 4-1 defeat by rivals Chelsea - had seen the north London side top the table with an unbeaten run.
After the news that the 26-year-old had withdrawn from the England squad on Friday, the Spurs boss confirmed what many fans would have feared - that the injury is "a lot worse" than they thought.
How costly will his absence prove to be?
Maddison has scored three goals and provided five assists in his first 12 games for the club. He currently sits fifth in the league for assists, and top among Spurs players.
According to Opta, the 26-year-old also sits fourth for big chances created in the league this season (six) - again the most of any Tottenham player.
His work in attacking areas and service into other players has been a key part of Spurs' success.
Maddison sits in the top 10 this season for crosses played, while comes in second only to Manchester United captain Bruno Fernandes for passes into the box. He is also fifth in the league when it comes to chances created from set plays.
It's perhaps no surprise then that the opposition have struggled to stop the former Leicester man. Experienced Crystal Palace forward Jordan Ayew is the only player to have won more fouls than Maddison's 30 in the league this campaign.
With Postecoglou's side suddenly finding themselves in something of an injury and suspension crisis, it could be Maddison's lay-off until the new year that proves most damaging.