Mbappe has struggled this season despite scoring seven goals in Ligue 1 for Paris St Germain.
PSG were crushed 4-1 at Newcastle United in the Champions League on Wednesday and Mbappe had little influence in the match at St James' Park.
"He's not at his best, just like his club's results. Obviously, with all he's capable of doing and his influence, that has a big impact on his team," Deschamps told a press conference.
"This isn't the first time, nor the last, that he's had periods when he's underperformed. Perhaps he didn't have a typical summer preparation."
Deschamps believes Mbappe will bounce back.
"But I'm not worried about him and his competitive spirit. I know him well. He must not be satisfied at the moment. Even when he does well, he wants to do better," he said.
France travel to Amsterdam to face the Netherlands on October 13th. They are top of Group B with a maximum 15 points.
