A victory for DR Congo on Monday would leave Tunisia, who can go through with a draw, relying on Cape Verde failing to record a victory in their Group B clash with basement side Zambia.
However, Leekens insists his players will push for a win in Ebebiyin - the location of Tunisia's quarter-final fixture should they top the group.
"If we go into the game believing we are in a favourable position, then we are making a mistake," he said. "We must play the game to win.
"DR Congo are fast, athletic and strong, but they are not our strengths. We are a more technical team.
"My players are great professionals, not the best players in the world, but they have a very good fighting spirit, they will give everything until the end.
"This is a very important match for our qualification and it will be a tough game, but DR Congo have to win and we want to win and we won't risk it."
Tunisia have won two of the three previous AFCON meetings between these sides, with the third ending in a draw, and DR Congo have just won just two matches in the competition since finishing third in 1998.
A draw on Monday would see DR Congo become the first nation to tie six AFCON games in a row, but coach Florent Ibenge believes his side have what it takes to make the last eight.
"Everybody can beat everybody," he said. "We must trust in our strength and in our abilities. We have to show it on the pitch.
"It is what I said to my players. They need to have confidence. They have to give everything they can.
"We must not have any regrets. We cannot leave the pitch shy.
"It's been two games already we've returned to the locker room with some regrets. We should have shown more spirit in order to get the victory."
DR Congo will be hoping Youssouf Mulumbu can recover from a groin injury in time to feature.
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