Gabon have been weakened by injuries to midfielder Mario Lemina and the full-back Johann Obiang.
If they win, Gabon will leapfrog group leaders Cameroon and advance to the last eight, but a defeat would make them just the fourth of 33 Cup of Nations hosts to be eliminated after the group stages.
Cameroon took control of Group A after coming from behind to beat Guinea-Bissau 2-1. Cameroon coach Hugo Broos said ahead of the showdown with Gabon in Libreville that his team would press for victory. "I think the biggest error we could make would be to play for a draw. That is too dangerous," Broos told Canal Plus Afrique. "We will go out to win without doing anything stupid. We need to be well organised but we won't just sit back and defend."
He added: "We will look to get a goal because if we can do that we will put Gabon in real difficulty."
Guinea-Bissau and Burkina Faso both have a chance to progress and they meet in Franceville. Guinea-Bissau – nicknamed the Wild Dogs - are appearing at their first Cup of Nations and they will go through to the last eight if they win and Gabon lose.
For 2013 runners-up Burkina Faso it is simpler. Victory will ensure their progress. Their task though has been complicated by injuries to key forwards Jonathan Pitroipa and Jonathan Zongo.