Arsenal's turbulent run took another twist on Tuesday night when they were dealt a 1-0 defeat by Inter Milan at the San Siro.
Mikel Arteta's side dominated large spells of the match but were left to rue a controversial penalty in first-half stoppage time when Mikel Merino was adjudged to have handled the ball.
Hakan Calhanoglu converted the ensuing spot-kick, and, despite bravely pushing for an equaliser, the Gunners fell to their second straight defeat in four days, and their first in the Champions League so far.
Arsenal's preparations for Wednesday's tie in Milan were overshadowed by the shock resignation of sporting director Edu.
Edu, credited with Arsenal's upturn in fortunes in recent seasons, scored in a thumping 5-1 win here, for Arsene Wenger's side 21 years ago. But on Wednesday, history did not repeat itself.
Arsenal's Premier League challenge has been knocked off course, and, amid a hostile atmosphere, and without the injured Declan Rice, the visitors might have fallen behind after just 100 seconds.
Wing-back Denzel Dumfries let rip with the outside of his right foot from inside the penalty area, and his fine effort rattled David Raya's crossbar.
Moments later, the Arsenal goalkeeper was scrambling to his right in an attempt to save Calhanoglu's shot from range. He breathed a sigh of relief as the ball fizzed narrowly past his far post.
Then, Mehdi Taremi's tempting pull-back across the six-yard box spelt danger. But William Saliba came to Arsenal's rescue.
These were nervy moments for the Gunners, who spent the opening 10 minutes firmly rooted inside their own half.
But after riding the storm, Arteta's men steadied the ship. Bukayo Saka's second corner of the game landed menacingly under Yann Sommer's crossbar, before the Inter keeper managed to punch the ball clear, clattering Dumfries in the process.
After 27 minutes, Saka registered his side's first strike on target, albeit a tame one, straight down Sommer's throat.
Gabriel Martinelli's inswinging cross then found Merino with the Spaniard getting his head on the ball, and taking a right hook from Sommer for his troubles.
Suddenly, the visitors were in control. Corner after corner followed - seven in all for Arsenal in the first 45, 14 without reply by the end - only for Inter to snatch a half-time lead.
Calhanoglu's set-piece skimmed off Taremi and then on to Merino's outstretched arm. Referee Istvan Kovacs did not hesitate in pointing to the spot.
Hakan Calhanoglu gives Inter Milan the lead from the spot 🎯
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Arsenal might feel hard done by after the penalty was awarded for handball 🤚
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Was Merino's arm in a natural position? A VAR check followed but it did not come to Merino's saviour.
Calhanoglu stepped up and sent Raya the wrong way in the third minute of stoppage time - the home side's sole shot on target in the opening period.
It proved to be Merino's final act with Gabriel Jesus sent on by Arteta at half-time.
Kai Havertz dropped back into midfield and the German found Martinelli immediately after the restart only for the Brazilian to fire into Sommer's side-netting.
Saliba them miscued his jump from Leandro Trossard's corner and failed to get anything on the ball when he probably should have done.
But Arsenal continued to look dangerous from set-pieces and shortly before the hour mark Gabriel met Saka's corner but the Brazilian's header was blocked on the line by Dumfries.
Sommer then tipped Havertz's curled looping effort around the post.
Arsenal were in the ascendancy but could not find the breakthrough against a team that has not shipped a goal in Europe yet this season.
Arteta was growing increasingly frustrated and he bizarrely ended up in the referee's notebook when he handled the ball with it still in play.
Arteta then courted Kovacs' attention again after Yann Bisseck went down under a challenge from Saka. The Spaniard escaped with a stern word.
The visitors continued to press and Havertz was provided with a golden opportunity to equalise in the 75th minute only to be thwarted by Bisseck's fine sliding tackle.
The Gunners were running out of time and all eyes turned to the bench to see if captain Martin Odegaard would be handed his first appearance since September.
He eventually arrived in the 90th minute - with Havertz unable to continue following a clash of heads - but he could do nothing to save his side.
