Last season Mauricio Pochettino fretted over Eric Dier's form. Then he discovered he had been approached by Manchester United.

And he was further incensed by Dier and Jose Mourinho chatting and laughing after a 1-0 defeat at Old Trafford.

Pochettino explains how he felt he refocused Dier on Tottenham...

Mauricio Pochettino (right) has revealed that he saw Eric Dier (left) talking to Jose Mourinho

Mourinho (left) and Dier conversed in Portuguese at Old Trafford back in December 2016

The conversation took place after Man United beat Spurs 1-0 and Pochettino was not pleased

I've told Eric he has what it takes to be the best English centre back but he has to be convinced of that himself. We've put the conditions in place for him to improve. But he broke into the national team thanks to his displays in the [midfield] holding role and ended up scoring a couple of big goals.

After we signed [Victor] Wanyama [in summer, 2016], Eric, who now sees himself as a midfielder, felt that we had treated him badly because Wanyama's arrival would halt his development. His performances have started to suffer this season. We've spoken a lot recently but I've felt he hasn't been telling me everything. Later on, I once again tried to understand why he couldn't shake off the shackles and I offered to help him with whatever it was.

Nothing. Then I found out that United have made an approach and the player is being destabilised. His people have been putting pressure on him, although United are not promising anything.

Mourinho and I had finished our interviews at Old Trafford [after the 1-0 defeat by Manchester United, December 2016] and the players were doing their warm-down on the pitch. When Jose was done with the press, he stood by the entrance to the tunnel and regarded the returning players.

Tottenham manager Pochettino was far from impressed with what he had witnessed

The next day Pochettino and Dier, who is a reported target for United, spoke for four hours

Pochettino made it clear that England international Dier would not be leaving his club

He greeted Moussa Sissoko and hugged Dier. They passed by me en route to the dressing rooms, laughing, speaking in Portuguese. Maybe it is a common Mourinho tactic, but he put Eric in a compromising position. You cannot do that after a defeat.

'Are you friends with Mourinho?' I asked him. 'No, but I've known him a long time, from my time in Portugal... one of his godsons coached me. He always says hello.'

I sat down with Eric after lunch on Monday and we chatted for four hours about the whole shebang: his agent, family, confusion.

As for the Mourinho incident, 'What could I have done?' Eric asked me.

He told me about United's interest since last summer [2016] and I explained the situation to him clearly.

'Look, you aren't leaving because you signed a five-year deal with us in August. You're among the highest-paid players at Tottenham at the age of 22. You're important to us and you could become the best centre back in the Premier League.'

Ever since that conversation, Eric admits that he could have waited for Mourinho to be out of sight before heading to the dressing room.

Dier faced United again six months later as Spurs beat them in White Hart Lane's farewell game

Utility man Dier played in midfield against United, which is what he believes is his best position

But Pochettino thinks Dier could become the best centre back in the Premier League

In January, Pochettino takes Dier aside again to focus him...

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He [Dier] has had a tricky six months. 'You aren't the same Eric as last year, the one from the Euros,' I told him in training earlier in the season. Recently, I spent the week discussing and speaking about what was happening to him.

Every day we looked at different things. For instance, I made a table for him with the headings Good, Very Good, Excellent and Unique. I wrote Maradona, Messi and Cristiano Ronaldo in the fourth one, before asking him where he saw himself.

'Very Good,' he said.

'Yes, that's where you are. It's only a short trip to Excellent.

'Where are you as a defensive midfielder? And as a centre back?' Eric thinks he's further ahead as a midfielder than as a defender. We had a long chat about that because I disagree. In the end, I said to him, 'It doesn't matter. If you give 100 per cent wherever you play, it'll go well.'

Some things footballers have to discover on their own.

As form improves in February, Pochettino notices a difference...

Dier has rediscovered his focus, making good decisions and understanding his limits. We must not forget he has only just reached the top. I recently saw him in the gym doing intense exercise. I went up to him and said: 'Eric is back.'

Pochettino asked Dier to rate himself compared Diego Maradona (left with a young Spurs boss)

Dier played in a three-man central defensive unit as Spurs drew with Real Madrid on Tuesday