Emery already had a selection headache after deciding not to select Sead Kolasinac or Mesut Ozil after the pair were left shaken up following a failed car-jacking last week.
The Gunners lost 2-1 to Lyon as a Moussa Dembele double cancelled out Pierre-Emerick Aubameyang’s opener.
But it was the sight of Lacazette, voted Arsenal’s player of the season last year, sporting a protective boot as he departed the Emirates that will have Emery concerned just two weeks away from the start of the Premier League campaign.
“It’s in his ankle,” Emery said of Lacazette’s injury after he was replaced by Reiss Nelson less than 15 minutes into the friendly clash.
“He will probably be assessed over the next few days – but it’s not serious.
“We are thinking it’s not important, he decided with the doctor and with me that it is better to take no more risk.
“He tried to continue playing but I think it was better in the pre-season to take patience.
“The doctor said to me he is going to check tomorrow but the thinking is that it is not important.”
Lacazette told French reporters he had twisted his ankle as he left the Emirates Stadium limping with a protective boot on his right leg.
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Emery opted against playing new signings Dani Ceballos and Gabriel Martinelli from the start, both coming on in the second half as the latter scored a scrappy goal only to see it chalked off for handball.
But it was the omission of both Ozil and Kolasinac from the matchday squad which caught the eye.
The club and both players insisted they were fine following an attempted car-jacking – but it is understood that Emery spoke to them ahead of the game and decided not to involve them.
“Every player is very important in the team, but also each moment and some circumstances give us a decision between the player and us,” said the Spaniard in his post-match press conference.