Being without several key players including star Kevin De Bruyne, Axel Witsel, Eden Hazard, and Thibaut Courtois, the Red Devils were held to a 1-1 draw in Brussels.
Although Dortmund’s Thorgan Hazard opened the scoring in the 20th-minute, a header from Kyriakos Papadopoulos sealed the result as a 1-1 draw despite a good performance from Belgium.
I'm very, very satisfied with some of the individual performances," Martinez said after the game. "It seems Jeremy Doku had exactly the same impact he had in March.”
Joining Rennes from Anderlecht for a $28.60m fee in October, the 19-year-old has registered 2 goals and three assists in his debut Ligue 1 season.
"He's looking always to be getting stronger and better. Not only when he has the ball but in general in many actions of the game he's involved in. He worked well tonight."
On the other stars of the match, the Spaniard added: "Yannick Carrasco was very strong in both halves of the field. Romelu Lukaku also showed that he was having a very good time mentally.
"Then there is Dennis Praet, for a player who has not played for so long, it's really nice to see that he managed the 90 minutes well. It's very good to see such a good response from all the players."
On his outcomes from the friendly tie against Greece, who have failed to qualify for Euro 2020, the former Everton boss said: "We needed a game like this," he said. "You don't learn anything that you win 3 or 4-0.
"I wanted a competitive team like the ones we are going to face at the Euros. That's why we chose Greece. We knew it would not be a friendly match against them.
"I am not disappointed because this game was not scheduled to be won. It was played so that all the players could level up.
"Many players have accumulated the playing time necessary for the Euros."
Belgium are drawn with Russia, Denmark, and Finland in Euro 2020’s Group B, and they will start their journey on June 12 in their tournament opener against Russia.