The France international was forced off after just 12 minutes against his former side.
Lacazette was replaced by youngster Reiss Nelson after appearing to pick up an ankle knock.
As the second half got underway, he was spotted sitting on the substitute’s bench wear a protective boot.
The image circulated on Twitter, making Arsenal fans nervous ahead of the new season.
“Please no, not Laca,” tweeted one concerned fan.
Another added: “Typical Arsenal. One of best players injured two weeks before the season kicks off.”
“How is Lacazette injured already?” contemplated a third.
But not all Gooners were so negative, with some trying to keep a positive outlook.
“If it was bad, surely he’d be removed for immediate treatment?” questioned one.
“If Lacazette does have a slight injury, we really need to sign Pepe to help Auba,” another added.
Pierre-Emerick Aubameyang gave Arsenal the lead with a smart finish after 35 minutes of the friendly game.
But the visitors struck back through Moussa Dembele to equalise midway through the second period.
Arsenal look set to splash £72m on Nicolas Pepe in their bid to qualify for the Champions League after missing out for the last three years.
The transfer fee will make the winger the third most-expensive player signed by a Premier League club.
Pepe ran riot for Lille in Ligue 1 last season, sparking interest from the likes of Liverpool and Manchester United.
The 24-year-old eventually netted 22 goals, second only to Paris St-Germain’s Kylian Mbappe, while also registering 11 assists.