Having suffered back-to-back defeats in the Premier League, it is clear that there is something missing from a Chelsea team that previously enjoyed a 16-match unbeaten run.
The new-and-improved defence remains, as do key midfielders N'Golo Kante and Mason Mount. Even the decision to switch out Tammy Abraham for Olivier Giroud has not diminished their goal threat from central areas.
It is elsewhere in attack, however, that things seem to have dropped off, with Hakim Ziyech's absence having been keenly felt since he limped out of the 3-1 win over Leeds United with a hamstring strain on December 5.
The Blues have not won any of their three games since that moment, including those losses against Everton and Wolves that saw them slip to seventh in the league table ahead of the weekend's fixtures.
Against both Carlo Ancelotti and Nuno Espirito Santo's sides, Chelsea struggled to break down their opponents before being hit on the counter attack.
At Goodison Park, it was Ziyech's fellow summer arrivals Timo Werner and Kai Havertz that were tasked with supporting Giroud from the flanks, with Christian Pulisic's return then allowing Havertz to move back into midfield at Molineux.
None of the trio was able to create anything of note, however, with full-backs Reece James and Ben Chilwell relied upon to put balls into the box that the opposition defenders largely handled with ease.
Werner, for example, is far more comfortable when encouraged to move towards goal from a wide area, but tasked with playing as a more traditional winger he has struggled, with the games against Everton and Wolves returning two off-target shots and just two key passes.
The Germany international has now failed to find the net in any of his last eight outings for club and country, and may need a game or two out of the line-up to take stock before being unleashed again over the festive period.
His compatriot Havertz, meanwhile, has looked even more out of sorts since his £70 million ($97m) summer arrival from Bayer Leverkusen, with his totals of no shots and a solitary key pass in the last two games only highlighting his struggles to adapt to the English game.
The same, fortunately for Frank Lampard, cannot be said of Ziyech, who has been a shining light despite injury having restricted him to just seven league appearances since his arrival from Ajax.
The Morocco international has an expected assist (xA) total of 2.33 so far this term, which ranks him as the highest among Chelsea's attacking players ahead of Mount, who sits at 2.13.
Ziyech has also created 2.4 chances per game in all competitions for his new club, with 1.6 of those per 90 minutes coming from open play.
The 27-year-old's presence has been key in Chelsea building on what was one of their biggest weaknesses last season, with the Blues looking far more capable of breaking down sides who play with low defensive blocks than they do in games without him.
Against both Burnley and Sheffield United, in particular, Ziyech was almost unstoppable, producing three assists as he looked to cut inside from the right onto his left foot, which in turn leaves space for James to create behind him.
"He shows his confidence on the ball. He is very technically gifted; he sees things a lot of players won’t see," former Chelsea and Ajax defender Mario Melchiot told Goal earlier this year.
"He is a left-footed player and it is very crucial, especially in the style of football we see now. He has a great long pass, he can score, dribble and in one-on-one situations, he will take you on."
That left-footedness and willingness to cut inside early rather than get to the by-line is perhaps what makes Ziyech unique within the Chelsea squad.
The likes of Werner and Pulisic are far more direct when they have the ball at their feet, but Ziyech's first thought is to look for Giroud or Abraham in the middle, or deliver the ball for the overlapping James.
Given he was the cheapest outfield player - aside from the free transfer of Thiago Silva - that Lampard added to his squad this summer, it is remarkable that the winger has become so important, so quickly.
It is hoped that after he returned to training in recent days that he could play some part against West Ham on Monday, and if last week's performances are anything to go by, Chelsea need him.
Whether it is via the eye test or the raw statistics from his performances, there is no doubt that Ziyech makes Chelsea tick.
