Nacho Monreal's surprise absence from the Arsenal squad in the Gunners' 3-1 victory over Leicester City was apparently due to injury.
Unai Emery's team came from a goal down against the Foxes on Monday night to secure their tenth victory in a row. Mesut Özil, who captained his side, cancelled out Hector Bellerin's own goal before a double from Pierre-Emerick Aubameyang sealed the victory.
However, one of Arsenal's most consistent performers in recent seasons, Monreal, was left out of the squad as Stephan Lichtsteiner started at left-back.
According to Arsenal's official Twitter account, Monreal had complained about some tightness in his hamstring and he was thus left out as a precaution.
It is uncertain whether the Spanish full-back will recover in time to face Sporting Club in the Europa League on Thursday night, in what will likely be Arsenal's toughest fixture in the group stage.
However, with a multitude of games coming up for the Gunners, Unai Emery is unlikely to take any risks with Monreal in fear that the injury might worsen and sideline the Spaniard for the foreseeable future.
In addition to their fixture against Sporting Club on Thursday, Arsenal face a tough trip to Selhurst Park on Sunday as they face Crystal Palace, with games against Blackpool and Liverpool also on the horizon.
In Monreal's absence, Emery opted to play the experienced Lichtsteiner, who was signed from Juventus in the summer, at left-back. However, 18-year-old Zech Medley was in the squad against Leicester and is another option should Emery choose to rotate on Thursday night.
After a consistent campaign in Arséne Wenger's final season at the club, Monreal came second in Arsenal's 'Player of the Season' award, finishing behind Aaron Ramsey.
Following the Gunners' 3-1 victory over Leicester, they next face Sporting Club in the Europa League on Thursday evening. Emery will be hoping to continue their 10-game winning run and extend Arsenal's 100% record in the Europa League.