Martial enjoyed a strong start to his United career since signing from Monaco in September, scoring 11 goals in 31 Premier League games last campaign but has been unable to find the back of the net under manager Jose Mourinho.
"Anthony started the season very early and he has already played a lot in a system that is different to ours. He needs to be more consistent despite his qualities," Deschamps told British media of the 20-year-old.
Martial made three appearances in Euro 2016 and Deschamps believes fatigue could have affected his performances in France.
"He's played a lot. He's the one who played the most last season and that's why he was a little unfit at the European Championships. He has a lot of qualities," the 47-year-old added.
Martial was named in Deschamps' 23-man squad for a friendly against Italy in Bari on Thursday and a World Cup qualifier against Belarus in Borisov five days later.