Arsenal's top scorer Aubameyang was sent off for a rash challenge on Crystal Palace's Max Meyer during their 1-1 draw on Saturday and Arteta said the striker would serve a three-match suspension after an appeal to reduce it to one game was rejected.
"It has been confirmed that he is going to be suspended for three games," Arteta told reporters on Wednesday ahead of 10th-placed Arsenal's league match against Sheffield United on Saturday.
"It's a big shame and a big loss for us because as well we know Auba's intention when he plays. But unfortunately he mistimed the tackle, he made a decision and we have to accept it.
"Players have to step up. You know, when one of your big players is not there, they have to take responsibility."
Lacazette, who has scored only five times in the league this season, is expected to lead the line but he has struggled for form and has not found the back of the net in six games in all competitions.
"You can help him (Lacazette) by talking to him and giving him confidence, but that ball has to end up in the net," Arteta added. "I think that's the best medicine for strikers.
"What we have to try to do is put Laca in positions where he can have as many opportunities to do that as possible during a game."
With the transfer window open until the end of the month, Arteta confirmed he had a wishlist but said there was "no truth at all" regarding media rumours linking Manchester City defender John Stones to the north London club.
"John is a player that I really like and I followed," the Spaniard said. "We signed him when I was at Manchester City and I worked with him for many years and know him well.
"When I look at centre backs he has many attributes that I like, but we're not interested."
Arteta said Sead Kolasinac (thigh) and Lucas Torreira (hip) are being assessed ahead of Saturday's game while Hector Bellerin, sidelined since early December with a hamstring issue, needs more training sessions before he is ready to return. (Reporting by Rohith Nair in Bengaluru Editing by Toby Davis)