Ajaccio have not won in 10 matches and sit second-last in Ligue 1 with just nine points from 16 matches but Ranieri said he is adamant third-placed Monaco must be 'focused and motivated' to defeat the Corsicans.
Ranieri was impressed by how Ajaccio performed in their 1-1 draw with Bastia in the Derby Corse on Wednesday where they fought back to claim a point despite losing Joshua Nadeau to a red card in the 62nd minute.
"When we play against Ajaccio, we will have to really concentrate; we'll need to be clever and play well with the ball and keep possession," the Italian coach said.
"Ajaccio did very well against Bastia. They drew that match, even though they were playing with 10 men against 11. So it's very important to be focused and motivated."
Ranieri has been impressed by his team's form over the past three games as they have beaten Nantes, Rennes and Nice.
After a poor spell from the end of October into the start of November, Monaco have pulled within two points of leaders Paris Saint-Germain, who lost 2-0 to Evian on Wednesday.
Ranieri wants another 'good performance' against Ajaccio as he remains hopeful of challenging for the French title, just a season after gaining promotion from Ligue 2.
"I want to win the Ligue 1 title this season," Ranieri said.
"I'm working hard every day, thinking about doing just that but I know that PSG are better than us."
Ranieri also confirmed Colombian striker Radamel Falcao will again be unavailable versus Ajaccio, after missing the past two matches with a thigh injury.
"Radamel Falcao is injured; it's an old injury that dates back from last year when he was with Atletico Madrid," he said.
"He has some inflammation, so he won't play this weekend against Ajaccio."
