Dembele is Tottenham's beauty and the beast - replacing him will test Pochettino
It is nearly two years since Mauricio Pochettino joked his side "do not exist" without Mousa Dembele but it is still difficult to imagine Tottenham without the Belgian, who has been described as a "genius" by his manager.
The club is prepared to listen to offers for Dembele -- who has a year remaining on his contract and wants a new challenge -- in the summer but replacing him will be one of the toughest tasks of Pochettino's four-year tenure.
Spurs have enjoyed standout results without Dembele this season, notably against Real Madrid in the Champions League, but the midfielder, equal parts beauty and the beast, remains integral to their play and they suffer when he is off-colour.
Pochettino's side were purring in the FA Cup semifinal against Manchester United before Dembele started hobbling. For all the wider reasons for that defeat, it was the performance of an out-of-sorts Dembele, who lost the ball to Paul Pogba for United's equaliser, that cost them as much as anything else.
It is immediately easy to spot when Dembele is not 100 percent because he actually loses physical battles and he still did not look fit for Monday's 2-0 win over Watford, succumbing to the skinny Will Hughes in a wrestling match within minutes of kickoff.
It was no surprise when he limped off with an ankle injury, which Pochettino said would be assessed, after an hour.
It is not inconceivable that Dembele has now played his last game for Tottenham. The midfielder, 31 in July, has said he will never play without pain and he sat out the final four league games of last season after Spurs had lost the FA Cup semifinal to Chelsea.
With less than two weeks until the end of the campaign, and a Champions League place very nearly secured, Pochettino may decide to spare Dembele the matches against West Brom, Newcastle and Leicester City, regardless of whether he is available.
Replacing a player with such a unique skillset would be difficult for any club but it will be particularly hard for Tottenham to find comparable quality on a tight budget, when there are other areas to address and a new stadium to pay for.
In autumn, Spurs appeared to already have a ready-made replacement for Dembele in Harry Winks but Pochettino does not expect the 22-year-old to play again this season due to a persistent ankle problem, which has plagued the midfielder since November.
Winks ran the show in the victories over Real, Liverpool and Borussia Dortmund before Christmas but there are now serious questions over his fitness after two campaigns interrupted by ankle injuries.
Winks, who has spent time at a specialist medical facility in Qatar recently, had hoped to be part of England's World Cup squad this summer but instead he will spend it trying to get fully fit and discomfort-free for the first time in over a year. His recovery is likely to have a bearing on Spurs' pursuit of a replacement for Dembele.
Eric Dier, at least, has been a constant in central midfield this season and the 23-year-old no longer looks like a player who would rather be at Manchester United.
But, happy or not, there are doubts about Dier's quality as a central midfielder. The England international has struggled against the very best teams, notably United a fortnight ago and Juventus in Spurs' Champions League round-of-16 defeat, and his occasional sloppiness in possession is a significant weakness: Liverpool and Mohamed Salah punished a loose Dier pass in Spurs' 2-2 draw at Anfield in February.
Victor Wanyama, meanwhile, has started just five Premier League games this season after a knee injury suffered in preseason and Pochettino will also hope to use preseason to try to restore the Kenyan to last season's levels, when he one of the most consistent midfielders in the country.
Pochettino has said he wants Spurs to make signings before the start of the World Cup on June 14, which leaves Spurs a window of just a month after the end of the final game of the season at home to Leicester.
Replacing Dembele is a daunting task but it has been made all the more complicated by the issues around Spurs' other midfield players and the limited time and resources available to Spurs.
Dan is ESPN FC's Tottenham correspondent. Follow him on Twitter: @Dan_KP.