Daichi Kamada's second-half brace secured a 2-1 Europa League win for Eintracht Frankfurt and piled further pressure on Arsenal head coach Unai Emery.
The Gunners are now without a win for seven matches across all competitions, with two rasping strikes from Japan forward Kamada adding to the impression Emery was on borrowed time at a sparsely populated Emirates Stadium.
Pierre-Emerick Aubameyang gave Arsenal a deserved lead at the end of a first half it dominated, with Granit Xhaka slotting back into the midfield for the first time since being stripped of the captaincy.
But the brittle nature of its collapse spoke of a club in turmoil and a positive result at Standard Liege in a fortnight's time may be needed to be absolutely sure of progress to the knockout stages.
Who might be in its dugout at that stage feels less clear.
Arsenal was on top early on. Bukayo Saka raided down the Frankfurt right in the 11th minute but Joe Willock and Aubameyang appeared to get in each other's way and the latter headed wide.
Gabriel Martinelli passed up chances to add to his haul of three Europa League goals this season when he shot too close to Eintracht goalkeeper Frederik Ronnow from a Xhaka corner and saw Gelson Fernandes clear his header from the subsequent set-piece off the line.
Ronnow dashed out to deny Saka when the winger darted in behind David Abraham, also saving from the teenage winger in the 41st minute.
David Luiz departed with a chest injury in between those two chances and Aubameyang blasted in via Ronnow's leg and the crossbar during the resulting period of stoppage time.
Martinelli played in Willock shortly after half-time but the midfielder misjudged his dinked finish and Ronnow was able to save.
It meant Kamada's spin infield and shot into the corner from the edge of the box in the 55th minute was against the run of play.
The same could not be said when Kamada was afforded ample room from similar range to dispatch a partially cleared 64th-minute corner.
To compound matters, Shkodran Mustafi hobbled off and Arsenal never recovered its poise. It remains to be seen whether Emery will be given the chance to recover his own poise.
What does it mean? Emery crisis at breaking point
If Emery could not get Arsenal back on track here, the obvious question was 'when on earth might he do so?'. A Frankfurt side it beat 3-0 in September was on a run of three straight defeats before this rematch and it lies 10th in the Bundesliga. What could possibly go wrong?
Well, a lot, as it happened, as the host missed chances to put the game to bed and suffered injuries before collapsing. Frankfurt coach Adi Hutter changed the match with the half-time introduction of Mijat Gacinovic and Dominik Kohr. In the circumstances, Emery's failure to adequately respond feels grimly significant for his own job prospects.
Kamada's double delight
If the space Arsenal afforded Kamada for his first goal was foolish, the room he enjoyed for his second bordered on gross negligence. Nevertheless, both finishes from the 23-year-old forward were of the highest order and the Gunners never recovered from his initial sucker punch.
Willock wastefulness proves costly
Arsenal's promising youngsters have generally proved immune to their club's wider disfunction on these midweek occasions, but the richly-gifted Willock found himself sucked in here. He either needed to finish or get out of Aubameyang's way early on and did neither, while his team-mates surely would not have unravelled to such an extent had he made it 2-0 after half-time.
Celtic tops group for first time
Celtic sealed top spot in Europa League Group E with a comfortable 3-1 home win over Rennes on Thursday.
Neil Lennon's men had already reached the knockout stage after matchday four, but Lazio's victory against Cluj ensured the Hoops will finish at the summit of a European group table for the first time.
Already-eliminated Rennes scarcely looked capable of stalling the host and Lewis Morgan and Ryan Christie had the Scottish Premiership champion two up at the break.
Mikey Johnston came off the bench to add a third, before fellow substitute Adrien Hunou grabbed a consolation for Rennes, but Celtic can look forward to a trip to Cluj with little on the line, while domestic title rival Rangers remains engaged in a tense group-stage tussle.
Feyenoord 2-2 Rangers
Braga 3-3 Wolves
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