The appointment of Pérez had been widely seen as one of the more astute managerial moves of the summer, with Villarreal tipped as potential surprise packages this season. Instead, the Yellow Submarine have endured a torrid start, culminating in a home defeat to newly promoted Deportivo La Coruña that has left goalkeeper Luiz Júnior particularly shaken by recent results.
Villarreal's difficulties have been compounded by defensive errors at both ends of the pitch, with the collapse against Deportivo following a pattern of squandered leads and costly individual mistakes that has undermined an otherwise talented squad.
The defeat leaves Pérez's side needing an urgent response as they prepare for a testing period that also includes their Champions League opener away to Borussia Dortmund.
Luiz Júnior's struggles have been symptomatic of a wider malaise at the back for Villarreal this season, with the Brazilian goalkeeper appearing to lose confidence as the goals have continued to go in. The club's coaching staff will be acutely aware that turning around his form, and that of the defence in front of him, represents one of the most pressing tasks facing Pérez as he looks to arrest the slide before it becomes a genuine relegation battle rather than the false start many still hope it will prove to be.
With the transfer window having closed and no further reinforcements available until January, Pérez has little choice but to work with the resources already at his disposal. The head coach has previously spoken of the need for his players to rediscover their conviction defensively, insisting there is no fundamental problem with the team's approach, but rather with individual execution in key moments.
Villarreal's home form in particular will be a source of concern, given that Deportivo arrived at the Estadio de la Cerámica as one of the division's newly promoted sides and left with a morale-boosting victory that further compounds Villarreal's difficulties.
Should results fail to improve quickly, question marks will inevitably begin to surface over Pérez's methods, despite the goodwill that greeted his appointment in the summer.
For now, the priority is a swift reaction, starting with the visit to Germany in the Champions League, where a positive result would go some way to easing the growing sense of anxiety around the club after such a difficult opening month of the season.