Arsenal head coach Mikel Arteta confirmed that Noni Madueke was withdrawn due to a knee injury in Wednesday's 0-0 Champions League draw with Sporting Lisbon.
The Gunners made history at the Emirates in the second leg of their quarter-final, where a goalless stalemate in the second leg of their quarter-final tie was enough for them to reach back-to-back UCL semi-finals for the first time ever.
Arteta's men struggled for ingenuity in the absences of Bukayo Saka and Martin Odegaard, though, while Madueke also failed to make the desired impact against Maximilian Araujo on the right flank.
The ex-Chelsea winger then came off worse in a collision with Sporting's Pedro Goncalves - which the referee decided did not meet the threshold for a foul - and stayed down by the edge of the pitch for a few minutes receiving treatment.
Madueke - who had already sustained one knee injury on England duty last month - was swiftly replaced by 16-year-old Max Dowman, handing Arsenal another untimely injury concern before Sunday's crunch clash with Manchester City.
Mikel Arteta confirms knee problem for Arsenal's Noni Madueke
Speaking to reporters in his post-game press conference, Arteta was customarily vague when giving an update on Madueke but did at least confirm that the winger had hurt his knee.
"I don't know, it was something in his knee, so we had to take him off, so I don't know," the Arsenal head coach said in a brief 20-word statement.
The fact that Madueke's injury stemmed from a collision offers hope of a swift recovery for the England international, who may have only suffered a contact issue rather than anything more sinister.
However, with Madueke now sustaining two knee issues in the space of a month and Saka still on the sidelines, the stage could be set for 16-year-old Dowman to start at the Etihad this weekend.
Arsenal are also sweating on the fitness of full-backs Jurrien Timber and Riccardo Calafiori for the trip to Man City, while Mikel Merino is definitely absent as he works his way back from a foot operation.
How can Arsenal replace Noni Madueke against Man City?
This time last year, Ethan Nwaneri would have been primed and ready to make an impact on the right-hand side for Arsenal, but the Premier League's youngest-ever player is currently trying to make a name for himself at Marseille.
Merino, Saka and Madueke's problems will beg the question whether Arsenal should have let Nwaneri depart in January, but it was central minutes that the youngster was after, not right-wing ones.
Dowman is the most natural alternative, and the 2009-born phenom has certainly done enough to earn a start vs. Man City in Arsenal fans' eyes, but whether he is ready in Arteta's is another matter entirely.
The Gunners boss could instead play it safe and deploy Gabriel Martinelli on the right-hand side, allowing either Leandro Trossard or ex-Man City striker Gabriel Jesus to function on the left flank.
Kai Havertz could be a wildcard option out wide too - the German often found himself on the right during Arsenal's build-up sequences last year - giving Arteta three alternatives if neither Saka nor Madueke make the cut.