Arkadiusz Milik wobbled gingerly on his left leg for another 10 minutes after winning Poland a penalty against Denmark in October 2016. He was substituted at the break, shot down with an ACL injury just over two months into his Napoli stay. Suddenly, Maurizio Sarri had to reassess his striking options at the Stadio San Paolo.
Resisting the urge to spearhead his attack with another angular marksman - Manolo Gabbiadini, a €13-million purchase in January 2015, was favorite to deputize for Milik - Sarri responded with a selection from left field. Dries Mertens, a diminutive winger signed by Rafa Benitez and then victimized by a rigorous rotation policy, was Milik's replacement.
Napoli finished that 2016-17 Serie A term with 94 goals. Mertens was deemed too small as a youth player at Anderlecht and was subsequently ignored by Gent, but slotted seamlessly into Sarri's pass-happy schematic as a false nine. His experience of infiltrating channels from the left flank was useful while he drifted out wide to jimmy space and create chances for teammates, and he would often return to the middle undetected. Last season, Mertens struck five more shots from inside the penalty area than Juventus' Gonzalo Higuain, the man Milik replaced at Napoli.
Sarri must miss Mertens' ceaseless activity and positional sense at Chelsea. Olivier Giroud and Alvaro Morata have combined for only five league goals and one assist, fueling suggestions that the club's next step in truly implementing Sarri-ball should be to buy a new striker.
Giroud and Morata's movement, or lack thereof, is an issue. While Mertens would zip around the park and pick at oppositions' seams, the Chelsea duo are static by comparison.
Giroud not managing a shot on target despite starting every match of France's victorious World Cup run over the summer is well documented, but more sympathetic viewers claimed his status as a sturdy target man helpfully detracted attention from his more energetic colleagues, such as Kylian Mbappe, Antoine Griezmann, and Paul Pogba.
But Sarri appears to be strictly adhering to his Napoli blueprint in west London - hence the swift purchase of Jorginho - and Giroud's shot-shy act is simply not good enough. While he can be a gifted link-up striker, his output is considerably lower than what Mertens mustered in Campania.
Morata is undeniably more mobile than Giroud, and Sarri voiced his support for the Spaniard earlier this week. "Morata is a quality player, fast and technically gifted," Sarri said.
Morata's top speed is decent, but his attempts to acclimate to Sarri's indefatigable, cohesive approach have fallen flat. The 26-year-old is getting caught offside with startling regularity: already 15 times in the current Premier League season. Aleksandar Mitrovic is the next-worst with 13 but has played 384 more minutes. Morata's movement and awareness require drastic improvement; Mertens appeared in all 38 matches of the 2017-18 Serie A campaign and was caught offside only 13 times.
Sarri would prefer to keep the ball on the deck but, for Giroud and Morata, heading is a main quality. Giroud won 69 aerial duels last term in a third of the minutes that Mertens counted in Serie A, while Morata took 54 airborne scuffles despite playing the equivalent of 10-and-a-half fewer league matches than the Belgian attacker. Standing at 5-foot-7, Mertens won just three aerial duels all of last season in Italy's top rung.
The service for an imposing target man isn't exactly forthcoming in Sarri's philosophy. Eden Hazard and Willian won't supply crosses; they'll instead weave, shimmy, and seek intricate, vertical passes into the striker's lane - very much reminiscent of Lorenzo Insigne and Jose Callejon's work at Napoli. Marcos Alonso is an immensely talented full-back, but a unique one in how he regularly prioritizes shooting over posting a delivery from his position.
Sarri wants a forward who can contribute to other phases of play, initiating and finishing attacks as a roaming frontman like Liverpool's Roberto Firmino, Barcelona's Luis Suarez, and Sergio Aguero after Pep Guardiola revived some of his old Independiente habits at Manchester City. Those individuals are a rare blend of aggression, skill, and tactical sense - and, admittedly, among the world's best - but Sarri was able to uncover those traits in Mertens after being inconvenienced by the first of Milik's two serious knee injuries.
If Giroud and Morata don't display a greater understanding of Sarri's expectations soon, the Italian - who prides himself on coaching what he has at his disposal - could delve into his resources to discover someone capable of fulfilling Mertens' false nine role. Failing that, the Chelsea boardroom will throw money at the issue.