Mourinho said he saw an improvement in Martial's work ethic in training ahead of the new campaign but the 21-year-old will need to do more on the pitch to impress him.
"Obviously we want more consistency in his talent," Mourinho told reporters. "I think today was positive for him, that's why I left him for 90 minutes on the pitch.
"He was enjoying it and trying things, it's important to try things in these friendly matches, so it's good for Anthony and his confidence.
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"I can say he is training better than before, he's working harder than before. It's just a question to bring his talent more in a consistent way."
United face Barcelona on Wednesday in Washington D.C. with a doubt over the fitness of midfielder Ander Herrera, who was substituted after suffering a knock in the second half.
"It must at least be very painful because for Ander to come off, it has to be very painful," the Portuguese added.
"I want to wait and see what it is...it was in front of the bench, it was a bad contact. Maybe it is his ribs but I don't know."
Mourinho is already without defenders Marcos Rojo, Luke Shaw and winger Ashley Young ahead of the season after the trio suffered long-term injuries at the end of last campaign.
United kick off their Premier League campaign at Old Trafford against West Ham United on Aug. 13.
(Reporting by Hardik Vyas in Bengaluru; editing by Amlan Chakraborty)
