The Gunners moved to bring in Aubameyang from Borussia Dortmund for a club-record fee, and the Gabonese striker was instantly installed as first-choice striker.
Lacazette, who was Arsenal's previous record signing, has been relegated to the bench for the last two games and missed a couple of late chances when being brought on in the 1-0 loss to Tottenham Hotspur.
Despite being overlooked for selection since Aubameyang arrived, Wenger has backed Lacazette to regain the type of form that made him such a big hit at former club Lyon.
"For him, one against one with the keeper, he is a good goalscorer," he told reporters after the defeat at Wembley. "He has gone through difficult periods before. He works hard in training, works on his finishing.
"I don't know what happened, did he not touch the ball well? It can happen, it is a fraction of a second. Maybe the confidence is not at its highest because he has seen a competitor coming in for him.
"He created two chances. That is a quality as well. He will score goals. He is a goalscorer, he scored goals in his whole career. He will score again."
Lacazette has scored nine goals in 26 Premier League appearances for Arsenal since joining for £46.5m last summer.