Lacazette came off the bench and missed a two late chances in Arsenal’s 1-0 loss to Tottenham in the Premier League on Saturday.
Since arriving from Lyon for €53 million in July, the Frenchman has scored just nine goals in 29 games in all competitions.
With Arsenal signing Aubameyang from Borussia Dortmund for £56m in January, Wenger said that may have dented Lacazette’s confidence.
“For him, one against one with the goalkeeper, he is a good goalscorer,” Wenger said.
“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.”
Arsenal face Ostersunds in the last 32 of the Europa League on Thursday.