It is April 5. The morning after a rough night before. Jose Mourinho admits he can’t sleep after matches. He sits at home, watching the video, pondering errors, plotting improvements. A few hours after a tactically outmanoeuvred Chelsea had drawn 1-1 with Valencia in London, their Champions League campaign, and with it, their manager’s future at the club are in peril.

Mourinho heads to his medical department, seeks out the club’s “rehabilitation physio” and delivers his nocturnal conclusions. “I need Essien,” the manager tells Thierry Laurent. “You have until next week to get him fit to play in Valencia.”

April 10, second leg tied at 1-1, Estadio Mestalla steeling itself for extra time, Michael Essien drives down Valencia’s left flank and collects a pass from Andriy Shevchenko. He shapes to cross, but notices Santiago Canizares drifting off his line. “I saw the goalkeeper try to anticipate the cross in so I just shot a quick one into the near post,” he says. “Normally you don’t score that kind of shot, but I was a little bit lucky and got that in.”

Fortunate or inspired, Essien’s strike let Chelsea complete the single most impressive away-leg recovery in European competition this season, reinstated Mourinho as the Champions League’s tactical tsar, and steered his team back en route to the quadruple.

Essien had injured himself keeping Chelsea in the FA Cup, straining the medial ligament of his right knee badly when 3-1 down to Tottenham, yet playing on through the first half, and refusing to be substituted at the break. “The doctor was asking the boss to substitute me but I told him, ‘I can, I want to play’,” says Essien. He carried on and at one point had a shot that inflicted further damage. “I grabbed my leg because it was just really painful, and we had no substitute left so I had to keep going. I really made it worse after the game,” he recalls.

Cue Laurent and the Frenchman’s specialised recovery programme. Chelsea have both the biggest medical department in the Premiership and a reputation for getting their injured players back on the field faster than any other club. When Mourinho prioritises a player, the attention to the task is startling. “I had one physio to work on me exclusively,” says Essien. “I’d go in every morning at, like, 10 and leave around five. I have to do massage, I have to work in the gym, ride on the bicycle, go out and do some endurance. It’s really boring. Sometimes I’d sleep at the training ground because I had to be there for so long.”

If a prodigious appetite for shut-eye — “13 or 14 hours on average” — and daily phone calls to mother Aba in Accra are two of Essien’s most endearing traits, an overzealous approach to tackling at one point threatened to stall his progress in England. The Ghanaian’s first months at Stamford Bridge after a £24.4m transfer from Olympique Lyon-nais were dynamic, with possession stolen and muscular runs past, or occasionally, through, opponents. Then, in a December 2005 Champions League group game with Liverpool, Essien raised his boot to claim possession and brought the weight of the world down on his head.

His tackle was poorly timed in three ways. First, in the most literal sense, going high and into Dietmar Hamann’s right knee. Second, in arriving 22 minutes into a goalless tie so devoid of spectacle it was highlighted in match reports and provided gruesome viewing and a talking point for television producers starved of highlights. Third, in coinciding with the height of dissatisfaction with Chelsea’s cocksure PR and pragmatic football.

One columnist demanded that this “high-paid hitman . . . be drummed out of the footballers’ union”. Embarrassed that their referee had failed to show a yellow card, Uefa deemed Essien guilty of “gross unsporting conduct” and suspended him for two games against Barcelona that saw Chelsea exit the competition. Though Essien publicly apologised more than once, he could not put his error to bed.

Sitting in a lounge of the Cadogan Hotel, Essien is all shy smiles and amused giggles, talking of his love of London and a Ghanaian restaurant in Tottenham where you should “eat jolof rice or fried yam. It’s good, but it’s heavy”. Then the Hamann incident is mentioned and he turns serious and reflective. “I think it was very unfair, I didn’t deserve that,” he says. “I think people do much more serious things than what I did, and I said I didn’t mean to do it. I didn’t like the way they treated me. It shocked me. I think they showed every one or two minutes on Sky TV — it was unbelievable.”

The European ban was preceded by an injury, and when Essien returned he was a more introverted footballer, questioning his natural style while opponents pressured officials into bridling it. “It affected my game. Any time I went in for anything the players would come out and the referee would just show some cards [there were three in his next six appearances]. It changed a little bit my game, but I think at the end I came back strongly to finish the season.”

Essien was suspended again for last week’s semi-final first leg, so his Champions League reacquaintance with Liverpool will be on Tuesday and he will strengthen the dominant Chelsea side that won 1-0 at Stamford Bridge. Mourinho can use him on the right-hand side of his midfield diamond, adding still more competitiveness to the centre, or at right-back, where Essien defends more robustly and counters more tellingly than Paulo Ferreira or Lassana Diarra.

Essien has played in every position in defence and midfield this season and carried out all with elan. Critics have turned into admirers. “I think the idea has changed,” he says. “They know the sort of player that I am, I’m not like this one who goes out to hurt people. I’m aggressive, yes, and as a midfielder you try to win every tackle, every ball, and that’s what I’m doing. I always go for the ball, not the man. When I was a kid they always told us: ‘You have to be first to to the ball’. And I think I still have that in mind.”

Amused again, Essien laughs at that the thought that his unusual, take-the-pass-ahead-of-the-striker approach to central defending is educated by the coach who trained him in Awutu when he was 12. He smiles once more when asked to describe his personality on and off the field.

There is a long pause. “I think I’m a very calm person, very shy,” he says. “I don’t talk much when I don’t really know a person. And I’m always happy — always smiling. When I’m on the pitch I’m a different man, I’m more aggressive and I mean business. It’s like I’m in the office — I have to work hard so on the pitch I look very different, I look much more aggressive. I don’t joke with my work.”

He can’t explain the difference: “Before the game I’m very relaxed. Sometimes I crack a few jokes in the dressing room, but as soon as I cross the white line everything changes. It’s just walking on the pitch, seeing the ball that does it.”

The man who kept Mourinho at Chelsea. All he had to do was show him a football.

TV match

Liverpool v Chelsea

Tuesday, ITV1, 7.30pm, kick-off 7.45pm