The Premier League leaders start Wednesday's last 32 second leg tie with holders Porto firm favourites to progress after securing a 2-1 advantage in Portugal.
But Toure does not expect Porto to relinquish their Europa League crown without a fight at the Etihad Stadium.
City's Ivory Coast international said that Roberto Mancini's men will have to play as well as they did in the first leg if they are progress.
"We'll have to play well again because the second game will be the same, very hard, although we'll have the advantage of playing in front of our fans," said the former Barcelona midfielder.
"It's not finished yet. Porto have fantastic players and it will be difficult, but we have to keep going and go through in this competition."
Argentina international striker Sergio Aguero could start for City after coming off the substitutes bench to hit a dramatic late winner in the first leg at the Estadio do Dragao.
Mancini's side had trailed to a Silvestre Varela goal before Alvaro Pereira scored an own goal to level the tie.
City are refreshed ahead of the deciding leg after a rare weekend without a game as they were knocked out of the FA Cup at the third round stage.
Meanwhile, Porto arrive in Manchester on the back of a 3-1 domestic away win at Vitoria Setubal which moved them to within two points of leaders Benfica.
Porto midfielder Lucho Gonzalez feels confident he and his team-mates have what it takes to overturn the deficit.
"Obviously, it's not positive when you lose at home in a two-legged tie, but we have what it takes to travel to Manchester and beat them," said Lucho, who rejoined Porto from Marseille last month.
"All of City's players have loads of quality, so that means you have to remain focused for the entire game - otherwise they'll make you pay for your mistakes.
"We need to play for 90 minutes like we did in the first half (at the Estadio do Dragao). It's the only way to beat a team like Manchester City."
Porto can draw encouragement from the fact that City have lost twice at home this season in domestic cup competition.
But the visitors are not helped by the absence of highly rated right-back Danilo due to a knee injury and Pereira's suspension.
Midfielder Joao Moutinho said: "It's a bad result for us to take into the second leg in Manchester, but now we have to raise our heads and keep on working, while thinking it's possible to get a positive result there and qualify for the last 16.
"We won't have Álvaro Pereira in the second leg and probably not Danilo either, but we have a great squad and the players our coach decides to use will give their best for us to achieve our goal."