Do not mention the Belgians. José Mourinho has heard one of them crop up over the past week or so and he did not seem to like it. The Chelsea manager was questioned about the omission of Kevin De Bruyne from his squads against Tottenham Hotspur and Steaua Bucharest and, on the second occasion, he stood up and left his press conference.

It is another of the club's Belgian contingent, however, who appears to pose a greater threat to his cool. Shortly after Mourinho had staged his exit in Bucharest, which he has insisted was not a flouncy walk-out, Romelu Lukaku continued his explosive start to his season-long loan at Everton, scoring twice in the 3-2 home win against Newcastle United. Roberto Martínez described him as "unplayable" and the Everton manager has had other nice things to say about Lukaku, particularly his game awareness and studious nature.

Lukaku marked his Everton debut at West Ham United by coming on as a half-time substitute to turn the game and head the winning goal, despite being temporarily knocked out as he did so. Having regained his senses, he asked the physiotherapist who had scored. The 20-year-old drew a blank at Fulham in the Capital One Cup but three goals in three appearances have not only fired excitement at Goodison, they have shone an unforgiving light on the toils of the strikers he has left behind at Chelsea.

Only Fernando Torres has flickered thus far, with a couple of goals and decisive performances but, as tends to be the case with him, there have been caveats. He was brilliant at Tottenham in the second half, for example, but he was sent off. As for the new signing, Samuel Eto'o, and Demba Ba, there have been no goals and no uprooting of trees. Ba feels like the forgotten man of Stamford Bridge.

Mourinho has heard a criticism to needle him, that Lukaku, with more goals than his strike-force put together, is showing him up. How could he have let him go? Martínez has confirmed that Chelsea have no recall clause, that the season at Everton means the season. With Torres now out for three weeks with the knee ligament strain he suffered against Steaua on Tuesday, the situation feels delicate.

Mourinho has refused to bite, maintaining that it was his decision to relocate Lukaku and one that would, in the longer-term, benefit Chelsea. One of his four strikers had to go out and if it was not Ba, whose deadline-day move to Arsenal broke down, it was to be Lukaku.

It still felt surprising that Lukaku was made available at the very last, sparking a clamour for his signature, although there had been mutterings about his sloppy performance in the European Super Cup against Bayern Munich on 30 August. It was not his crucial miss in the penalty shootout, rather his indisciplined cameo as an extra-time substitute.

He had also flattered to deceive in some of Chelsea's pre-season fixtures against the more established clubs. Mourinho's conviction hardened that Lukaku was not quite ready, that the best thing for all parties would be for him to develop elsewhere. "It is one thing to play for Everton and another thing to play for Chelsea," Mourinho said. "There are no regrets."

Lukaku has a point to prove. He said so when he was presented at Everton, where he has wasted no time in displacing Nikica Jelavic as the focal point of Martínez's team. He appears determined to turn the screw on Mourinho and ensure that he begins next season as the manager's first choice at Stamford Bridge. Before that, he intends to have starred for Belgium at the World Cup finals.

The bottom line was that he had to play this season. Even before Chelsea signed Eto'o, Lukaku was worried that he might not feature more regularly than once every three games and his World Cup could be jeopardised.

Lukaku's goal has not changed; he has simply had to take a further detour, following his productive loan at West Bromwich Albion last season. He continues to target the starting centre-forward's spot at Chelsea, to assume the responsibility that his hero Didier Drogba previously carried. Lukaku dreamed the dream well before he joined Chelsea from Anderlecht in 2011 for £18m and he has the evidence to prove it.

In the TV documentary De School van Lukaku, which followed his life at Sint-Guido-Instituut, with which Anderlecht have an educational link, he took a field trip to London in 2010 and he was filmed at Stamford Bridge, gazing out from the stands. "The day I play here in this stadium will be the single time in my life that you would see me cry," the Chelsea supporter said. "I'm going to succeed. I will play here some day."

Lukaku's focus is clear; the maturity beyond his years. He says he watches every single match in the Premier League in order to learn, to study movements and Martínez is astonished at how this young boy is "like a manager". Lukaku is consumed by the game. In Marbella last summer, he tweeted a picture of a small pitch, said that he would be playing there the following day and invited all-comers. There was quite a turnout, which included Jan Vertonghen and a couple of other Belgian players.

Lukaku's mission resumes at Manchester City on Saturday, when he will face his Belgium team-mate Vincent Kompany. Phil Jagielka, the Everton defender, feels that Lukaku has "taken us up to that next level". The awkward questions for Mourinho are likely to persist.