Belgium trail pool leaders Italy by three points and second-placed France by two at the midway point in the group, needing to finish in the top two to qualify for the quarter-finals.
Defeat at home and an expected win for Italy over Israel could effectively end their hopes of reaching the knockout stages with two rounds left to play.
"We must be brave against France. We won't get many opportunities and we have to finish the ones we get," Tedesco said.
"We won't be able to put pressure on them for 90 minutes, so it's also important to defend well in our own box. It's going to be a big game."
Belgium, who are without Kevin De Bruyne and Romelu Lukaku after they asked not to be considered for this international window, earned a 2-2 draw in Italy on Thursday having been two goals behind inside 24 minutes.
Tedesco is hoping his side will start better against France, who won 2-0 in Lyon when the teams met last month.
"We didn't start well (against Italy)," he said.
"We wanted to be compact, but we were way too impatient. And that quick (first) goal did not help. We are just human. It is in my character to also talk about the bad things. We must not hide that.
"But the match lasted 90 minutes, not half an hour. I want to emphasise that we showed a good response. With this young group, it was anything but a bad result against Italy."
Belgium have not beaten France in a competitive match since a World Cup qualifier in 1981. Their two victories since then have both beaten in friendly fixtures, the last in 2015.
"Will the poor results against France from the past discourage us? It can be a motivation. We can actually write history," Tedesco said.
"Of course, we will need a fantastic day. If you see who France can select. Then it doesn't really matter that (Kylian) Mbappe isn't there."
Mbappe has also asked to be excused from French duty for the October international window.
