Bayern Munich striker Mane's withdrawal from the squad ahead of the tournament after failing to recover from a leg injury dealt a massive blow to Senegal's chances of making an impact in Qatar.
The Lions of Teranga lost their opening game 2-0 to the Netherlands in Mane's absence, and face a must-win clash against hosts Qatar on Friday.
Chelsea defender Koulibaly said Mane, the African Player of the Year, has been in daily contact with the squad and is "keeping the mentality high" among the players.
"Even if he is not with us today in Qatar, he is speaking with all the players and this is really important for us," Koulibaly said.
"We know the importance that he has for the team. This is the good spirit, the good mentality, because we need it, and we hope that he will continue to be behind us."
Koulibaly said that when Mane speaks, "all the team and all Senegal are listening".
The defender also backed goalkeeper Edouard Mendy, his team-mate for club and country, to come good after a shaky opening performance against the Dutch.
"Edouard is a very important player for us," Koulibaly said.
"It's normal to go through difficult patches and I think we're making a mountain out of a molehill here.
"I am not worried. I know that Edouard will be on top of his game tomorrow and I know my team-mates feel likewise."
Senegal coach Aliou Cisse backed his misfiring strikers to find their scoring boots against Qatar.
"I don't have the slightest doubt about my players' ability to score goals," he said.
"Playing football, you need to be efficient and you need to have the right mindset. You need to keep a cool head in front of goal.
"I hope we can score a lot of goals."
Check the 2022 World Cup schedule and groups standings.
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