Mikel Arteta has explained that he substituted Leandro Trossard because they did not want to take any risks after the player felt something.
Noni Madueke replaced the Belgium international ten minutes before half-time and after the break went on to score what proved to be the winning goal. While he and fellow substitute Gabriel Martinelli ensured the Gunners took all three points, concern afterwards turned back to Trossard.
Arteta said: "With Leo, we don't know. He said he felt something, we didn't want to take any risk, obviously."
Arsenal visit Stamford Bridge on Sunday evening, one of five matches they play in the next 13 days. After that, they host Brentford at Emirates Stadium, followed by away matches against Aston Villa and Club Brugge in the Champions League, before welcoming Wolverhampton Wanderers in mid-December.
The Gunners already have a depleted attack without Gabriel Jesus, Kai Havertz and Viktor Gyokeres. Gabriel Magalhaes is another key player now sitting on the sidelines.
He had been ever-present before an injury sustained playing for Brazil meant the defender missed Sunday's North London Derby win over Tottenham Hotspur. Trossard could now be the latest previously always-available player to go down.
The timing of this setback also comes at a time when the forward was in his best form all season. All three of his Premier League goals have come since domestic affairs resumed after the October international break.
Similarly, all but one of his three assists have also come during this period. His productivity peaked in the 4-1 win over Spurs when he scored the opener and set up Eberechi Eze for the fourth.
Trossard has five goals and as many assists in 16 appearances across all competitions thus far this season. Bukayo Saka and Viktor Gyokeres are the only players to score more, with six strikes, while Declan Rice has just one more assist in far more minutes.
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