The striker picked up the nickname at former club Sporting Lisbon having scored five goals in his last three games against Porto, who are called the Dragons. He netted in his final appearance for Sporting, against Porto, when they won 2-1 last month before he completed a club record £29 million (€33m) move to Leicester on deadline day.
The Portuguese side, the 2004 Champions League winners, come to the King Power Stadium already trailing the Foxes by two points in Group G after the opening round of fixtures.
Slimani scored twice on his Premier League debut for Leicester, a 3-0 win over Burnley, and while Ranieri was unaware of his nickname he knows the Algeria international has put Porto to the sword before.
He said: “He’s a goalscorer and has scored a lot of goals against Porto and I’m sure he’ll be a threat to them. Slimani scores so many times against Porto I am thinking if he’s going to play or not.
“Yes, I spoke with him about Porto. We have a lot of respect for Porto, they are a more experienced team in Europe than us.
“They have played so many matches in the Champions League and are used to staying at the top of their league and have won six titles in the last 10 years. We respect them a lot but we also try to win. Both teams want to win.”
Leicester won their opening Champions League game 3-0 at Club Brugge two weeks ago, as Porto drew 1-1 with FC Copenhagen, after a heavy 4-1 defeat to Liverpool. This time they head into the game having lost 4-1 to Manchester United after conceding three goals from corners.
Referees have been told to stamp down on holding and grappling in the box this season and while Ranieri insisted it is not a new rule, he admitted his players are scared about conceding penalties.
Turkish official Cuneyt Cakir, who takes charge tonight, has handed out 11 yellow cards and one red in his last two games.
“Yes, we concede a lot of goals,” Ranieri said. “I spoke to players yesterday and they were scared. What the referees speak about is not a new rule, it’s something we’re used to doing. I said why change?
“Last season we were one of best in league and conceded very few goals from the set pieces and now we leave four metres. Now I can’t jump? We have to go back to our strengths.”
Leicester are tipped to get out of the group following their opening win in Belgium where Marc Albrighton scored their first-ever Champions League goal before Riyad Mahrez’s double settled the game.
Winger Albrighton admits the Foxes are having to adapt to being champions after being underdogs last season before their stunning 5,000-1 title triumph, but thrive on defying the odds.
He said: “Obviously last season it was nice to be the underdogs. Everyone was writing us off every game. It was good to defy the odds and go on to win those games. I wouldn’t say we are feeling the pressure of that. We have had a tough start to the Premier League campaign — we have played Arsenal, Manchester United and Liverpool and they are tough games.
“Obviously the manner in which we have lost is not good but to say we prefer being underdogs isn’t really true. We go into every game the same. In the Champions League, it will be no different. We are probably underdogs again but it will play no part in our mindset. We will try and win the game as we always do.”
Kasper Schmeichel could return after a muscle strain but Nampalys Mendy continues to be sidelined with an ankle injury but could be available for Sunday’s Premier League game against Southampton.
Meanwhile, Porto manager Nuno Espirito Santo is determined to improve the club’s wretched record in England. The Portuguese side have lost 14 out of 16 European games in England.
Porto’s best result came in 2004 when Costinha scored a 90th-minute equaliser to earn a last-gasp 1-1 draw at Manchester United, best remembered for Jose Mourinho’s touchline celebrations, to knock the Red Devils out of the Champions League 3-2 on aggregate.
Porto went on to win the competition that season and Nuno knows they must improve their results in England this year.
He said: “History tells us FC Porto has never managed to win in England but records are there to be broken. We have a chance in front of us. Leicester are champions of the Premier League and it is one of the best leagues in the world. What Leicester did last season was remarkable and we must respect it.
“It’s a new day and a new game and we have to go into it believing we can go beyond our limits.
“We know what Leicester can be and they are a very strong opposition. We know their strength and know what they can do but we have our knowledge about their team.
“We know who we are going to play tomorrow, we know the difficulties we are going to face and must never forget we are going to play against the Premier League champions.”