The Foxes progressed to the first knock-out round of the competition courtesy of a 2-1 win over Club Brugge at the King Power Stadium on Tuesday night, Shinji Okazaki and Riyad Mahrez both on the scoresheet in the first-half.
Victory - coupled with Porto's goalless draw with Kobenhavn, meant that Leicester finished as Group G winners with a game to spare, acting as welcome respite from a rocky league campaign.
Ranieri's side fell to a 2-1 defeat away at Watford at the weekend, their sixth loss from 12 games this term already - twice as many as they suffered on their way to winning the title last year.
And with Leicester now without a decisive Champions League tie until at least mid-February, the Italian manager insists his side need to focus on arresting their domestic decline.
Leicester boss salutes progression to knockouts
Ranieri told his post-match press conference: "It's unbelievable. Top of the group. Wow.
"I'm very happy and very proud for my players. I'm very happy for the chairman, for the fans and for everybody. Another journey, this time to the knockouts. Unbelievable."
Ranieri added that it was "very important" to finish top of their group, although his side could still be paired with the likes of Bayern Munich or Real Madrid.
But he insisted that their minds must now "go on to the Premier League", declaring: "I want to push my players to think about the Premier League. Our job is done now. We're through the group."
The City boss explained that no matter which team they face in the next round in Europe, they will be "a fantastic team" and they are simply "very happy" to progress.
But Ranieri reiterated that Leicester must once again concentrate on their form in the Premier League, where they currently sit 14th after a disappointing start.
"We are very close to the relegation zone and we must play at the same level as we have in the Champions League," continued the manager. "Because when we want to do something, we achieve something."
Ranieri also admitted that his team are "lacking confidence" in their league fixtures, explaining that "when something happens" their opponents "score a goal."
He suggested that Brugge scored "at the first chance" with "their first shot", which he called "unbelievable."
Foxes must change negative mood, says Ranieri
Ranieri revealed that he was confused by the second-half performance of his side. Leicester had controlled throughout the first period, with the gulf in quality well apparent.
But Jose Izquierdo's 40-yard run and finish halved the deficit on 52 minutes and although Leicester had plenty of chances before full-time to extend their advantage, the final stages were nervier than they needed to be.
Ranieri insisted his team were "very strange" having played "so well", saying that they "had 70 per-cent of the possession and created a lot of chances."
"But when we concede a goal on the counter-attack, why? An Italian manager conceding a goal on the counter-attack. I got crazy," Ranieri admitted to journalists.
He acknowledged that "that is football" and insisted that the Foxes "lost our heads" from that point on, adding: "Why? Keep going. Stay calm."
The Leicester manager felt that his side "lost another couple of chances" though praised his team for creating "another two or three chances" and finishing "well" and said they "have to change this mood."
Ranieri also declared that it is "not important" whom they face in the next round when asked who he might prefer to be paired with. Instead, he insisted that it is simply "important to be there in good condition."
"It will be another fairytale. Win, lose, it's not important," he continued. "It's important to go there."