The French striker was replaced with 20 minutes remaining of Sunday's 1-1 draw with Fulham.
"Lacazette has done his hamstring, it's not good news," Arteta told the club's website.
"That's why we rotated some players, because some players weren't recovered yet. But we cannot change all the players, so it's tough to see."
He added: "We'll have to see [how long he will be out for].
"We'll have the scan, probably on Tuesday, to see the extent of the injury and the timeline for it. But I don't know.
"I cannot tell if it's going to be a week, two weeks, five weeks or six weeks. He felt something in his hamstring and we don't know the extent of it.
"We are all disappointed because we all know the moment that Laca was on."