LONDON • The combination of players' post-World Cup breaks and the early transfer window have made this an extraordinarily difficult summer for a coach to move to a new club in a new country, assess his squad, instruct them in a completely new tactical system and make desired personnel changes.

Add the speculation swirling around several members of Chelsea's dressing room, the drawn-out process of officially appointing him, and Maurizio Sarri's task at Stamford Bridge appears particularly formidable.

Fortunately he is not prone to overhyping his likely impact. Back in 2015, when he was first approached by Napoli, he delivered an unusual sales pitch.

"We're going to lose our first seven games," he told Aurelio de Laurentiis.

"I laughed," the club's president later recalled. "He smiled. The understanding between us was born in that moment."

De Laurentiis might not have been laughing when Napoli did indeed lose their first game, to Sassuolo, and followed that with a pair of unconvincing draws.

He approached Sarri again, wondering if it might be worth moving away from the narrow 4-3-1-2 formation that had worked well for the coach in the past but seemed unsuited to Napoli's squad.

"President, let me do it my way," Sarri replied. "We might lose the first seven games, but then you'll see what happens."

Should anyone lose their first seven games at Chelsea, it is fairly obvious what would happen but, happily, Sarri's subsequent success makes it seem extremely unlikely.

In the end, he did change his formation for Napoli's next game, starting with a single striker and two wingers. They won 5-0, and then did it again in their next match.

"The switch to 4-3-3," de Laurentiis concluded, "happened because of me."

Sarri has stuck with 4-3-3 ever since and, from Chelsea's pre-season friendlies, appears determined to use it again at Stamford Bridge.

The Italian's tactics worked phenomenally well in Naples last season. They might have lost the Serie A title race narrowly to Juventus but, in Europe's top five leagues, only Real Madrid, Bayern Munich and Manchester City averaged more shots per game than Napoli; only City, Bayern and Paris Saint-Germain bettered them on possession, only City played more passes and only at City, Liverpool and Juve were goalkeepers forced into fewer saves. If Sarri can bring this style to Chelsea, the results could be genuinely thrilling.

"I love this philosophy," Chelsea defender David Luiz admitted.

"We play high, with lots of possession of the ball, in a technical way. He's trying to help us every single day to learn his philosophy quickly, to do our best for Chelsea.

"A new philosophy always takes time, but it also depends on us. If we are dedicated every day in training, we can try to learn quickly."

The arrival of "Sarriball", as Napoli's technical, high-speed style of play was christened, will be widely celebrated. Importantly, it is not only intended to be successful, but to be joyful.

"My goal is to have fun as long as I am here and be competitive in all competitions," Sarri said.

"Ours is not a sport, but a game, and anybody who plays a game starts doing that when they are young because it is fun. The child in us must be nurtured because this often makes us the best."

This prioritisation of pleasure comes in complete contrast to Chelsea's last couple of managers.

The difference between the miserable demeanour exhibited by his predecessor-but-one, Jose Mourinho, this pre-season and the man who now sits in the Chelsea dug-out is jarring.

It is hard to imagine the Portuguese asserting, as Sarri does, that the most important thing in life is "to have fun while you do your job".

But the Italian's arrival will not be celebrated by everyone at Chelsea, and the tactical overhaul will inevitably have casualties.

Perhaps the great beneficiary of Antonio Conte's switch to a 3-5-2 formation was Victor Moses, who sprang from relative obscurity to indispensability almost overnight. He appears likely to make the same journey in reverse now, while Cesar Azpilicueta returns to right-back.

Meanwhile Chelsea have been repeatedly linked with centre-backs, most frequently Daniele Rugani, which appears bizarre given their wild surfeit of options in that position, the fact that this year they will play with only two, and Sarri's insistence that the transfer market is "a refuge for weak coaches" and that he will instead focus on "growing the players we have".

THE GUARDIAN

CHELSEA'S TRANSFER BALANCE

-£46.9m

KEY SIGNING: JORGINHO

Midfielder (Napoli, £50.4 million or S$89.5 million): He knows everything about new Chelsea boss Maurizio Sarri and his preferred 4-3-3 formation, having played under him at Napoli. That would be a huge advantage as the Brazil-born Italian made an instant impact on his Blues debut in the 1-0 win over Perth Glory, touching the ball 101 times and making 98 successful passes in just 45 minutes. Jorginho will be the link between the players and their new manager, and has shown he can get the attack going in Sarri's high-pressing style.

KEY PLAYERS IN

• Rob Green, goalkeeper (Huddersfield Town, free)

KEY PLAYERS OUT

• Jeremie Boga, midfielder (Sassuolo, £3.5m)