Dele Alli is reportedly ‘upset and confused’ after he was left out of Tottenham’s matchday squad for Sunday’s Premier League clash against Southampton.This is according to The Sun, while The Telegraph understand that Paris Saint-Germain are in talks to sign the England midfielder.Dele, who was substituted at half-time in Spurs’ Premier League opener against Everton last weekend and left out of the squad to face Lokomotiv Plovdiv in mid-week, could leave the north London outfit before the transfer window closes on October 5.It was also reported on Sunday that Jose Mourinho wants to sign Manchester United midfielder Jesse Lingard, potentially as a replacement for Dele.This news has come as a surprise to many, but Lingard did enjoy the best spell of his career under Mourinho at Old Trafford.But the big question is: why has Dele suddenly fallen out of favour with his manager?Asked about his decision to leave the 24-year-old out of the squad to face Southampton, Mourinho told reporters: “We have a huge squad with numbers that are very difficult to manage. We have too many players for some positions and some of them are paying the price for this."

That still doesn’t explain why Dele has gone from one of the first names on the teamsheet to out of the squad altogether.

But does the recently Amazon documentary ‘All or Nothing: Tottenham’ provide a few clues as to why Mourinho’s opinion of Dele may have diminished?

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In one clip, Mourinho calls out the midfielder during a team-talk for being a “f***ing lazy guy” in training.

“Fast ball, fast ball and in the space,” Mourinho says after pausing a clip.

“Okay, I understood already, where’s Dele? I understood already that you are a f***ing lazy guy in training.”

Mourinho then speaks with Daniel Levy and tells the Tottenham chairman ‘we need to find motivation’ for Dele.

"I told already Dele very directly that he doesn't train well, he is not a good trainer,” Mourinho said.

"I am not saying a disaster but I am not saying Harry Kane, Harry Kane is a very good trainer.

"Sir Alex Ferguson gave me only one bit of advice in two and a half years: Buy Dele Alli. 'That guy, with that mentality, the way he plays, the aggression he has in mind. This guy is the Manchester United player. Buy Dele Alli'.

"And he [Ferguson] has an eye for a player. But he [Alli] is not a good trainer, we need to find motivation for the guy."

Perhaps Dele’s effort - or lack of - in training has failed to improve in recent weeks and Mourinho has had enough.

In another episode, we see Mourinho calling Dele into his office for an honest face-to-face conversation.

The Portuguese coach tells Dele that it’s down to him to fulfil his huge potential and nobody else.

"Maybe, inside, you are telling me to f*** off, but I have to tell you exactly what I see," Mourinho tells the midfielder.

"I have no doubts about your potential. I saw you do incredible things in incredible matches. But I always felt that you had ups and downs.

"There is a huge difference between a player who has consistency and a player who has moments. That is what makes the difference between a top, top player and a player with top potential.

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"It is something to analyse yourself for you to realise why your career has been MK Dons, Tottenham, national team... bang!

"Then, when you reached the top, why do you have these little ups and downs.

"I don't know if it is to do with your lifestyle - if in one period you were an amazing professional but in another period you felt you had become a party boy.

"I have no idea - only you can know that.

"I am 56 now and yesterday I was 20. Time flies.

“One day I think you will regret it if you don't reach what you can reach.

"I am not expecting you to be the man of the match every game. I am not expecting you to score goals every game. I want just to tell you that you will regret it.

"You should demand more from yourself. It should not be me demanding more from you.

"Nobody else. You. You should demand more from yourself."

You can only suspect that Dele, at least in Mourinho’s opinion, has failed to take his manager’s words of advice onboard.

And as a result, his Tottenham career could be about to come to an abrupt end.