Arsenal's 3-0 defeat to Liverpool was damaging for a number of reasons.
The Gunners put in arguably their worst display of the season to "shock" Mikel Arteta and blow all the momentum built up by a thrilling comeback from 3-0 down against West Ham before the international break.
Perhaps the most devastating blow of all that night though was the fact that Kieran Tierney was forced off with a knee injury that looks likely to rule him out for the rest of the season.
The Scot has been Arsenal's top chance creator from open play this season and speaking after the length of his layoff was confirmed, Arteta admitted his absence would necessitate a degree of adaptation in the way the Gunners attack their opponents.
”We’re going to have to make some adjustments because his qualities are unique and we don’t have anybody with his qualities within the squad unless we start to move a lot of pieces," said the Spaniard.
“Without any time to train, it is a little bit dangerous to do.
"But we’re going to have to find different ways to fulfil that gap and use other things that can be as effective as well."
Initially, Cedric was the man chosen to fill the void at left-back before Granit Xhaka stepped in adeptly in the victories over Sheffield United and Slavia Prague.
Neither though were able to replicate the aggressive attacking runs Tierney makes so effectively into the final third, where he offers such consistently dangerous delivery.
The man who was though was Nicolas Pepe.
The Ivorian has largely specialised on the right wing for Arsenal since his £72million transfer from Lille last season, but at times this season, he has excelled on the left.
When assisting Alexandre Lacazette's second and the Gunners fourth against Slavia Prague on Thursday, it was interesting to note Pepe's ability to drive down the left and whip in a pinpoint low cross.
Compare this to Tierney's assist for Lacazette's second goal the last time Arsenal netted four against West Brom - and the similarities are plain to see.
The Scot picks the ball up on the left side before driving purposefully down the wing and pumping a low ball into the box for the 29-year-old to turn home.
Arteta looks to set up his side with a five across the front line when they are on the attack in a manner similar to what Pep Guardiola has done so effectively at Manchester City.
The objective of this is to make the pitch as big as possible and stretch the opposition defence to create gaps that other players can drift into and exploit.
To achieve this though, a degree of width is required, which is normally where Tierney fits in overlapping Pierre-Emerick Aubameyang, Willian, Emile Smith Rowe, Gabriel Martinelli or whoever happens to be playing on the left wing for Arsenal that day.
In his absence though, and with Granit Xhaka incapable of replicating the Scot's ability to bound tirelessly up and down the pitch, Pepe was asked to maintain that crucial width and Slavia - who before Thursday night had conceded just three goals at home in European competition this season - simply could not cope.
Of course, what the Ivorian offers is different to Tierney's unique threat down the left.
As a forward player Pepe is far more prone to drifting into the half-spaces in between the full-back and the centre-back. It was from there that he scored his goal on the night.
But by having a left-footer playing on the left-wing, Arteta seems to have found a way of sticking to his core attacking principles without the player who is arguably most important to them.
When Tierney was out for a period in between January and February earlier this year, Pepe came into the side and put in outstanding goal-scoring performances against Southampton and Wolves when playing from the left-wing.
Now that Arsenal's first-choice left-back is out again, it seems the Ivorian is ready to step up and deliver in a time of need once again.
