A 1-0 home win, or victory by at least two clear goals, on Wednesday would send Dortmund into the semis to face either holders Bayern Munich or Paris Saint-Germain.
Aguero, who has netted 257 goals in 384 appearances and won four Premier League titles, one FA Cup and five League Cups at the club, is set to leave when his contract expires.
"I don't know what's going to happen but at these prices we're not going to buy any striker," Guardiola told reporters ahead of Saturday's league trip to Leicester City.
It is a rarity in these days of tactical complexities to see a team line-up with a genuine strike duo, but Leicester have bucked the trend of late, with Iheanacho emerging as possibly the key component in their run-in.
The 34-year-old Vardy, last season's Premier League Golden Boot winner, has managed one league goal this year.
Aguero went on to score 23 goals in 2011-12, with only Robin van Persie (30) and Wayne Rooney (27) scoring more that season.
Remarkably, for a man who has scored 181 Premier League goals to date - the most of any foreign player in English top-flight history - that iconic moment remains Aguero's only stoppage-time winner in the competition.
"No I'm not worried, because Joao is young, a goalkeeper without experience, but he has a lot of quality. I'm not worried for the absence of the two goalkeepers," Ancelotti told a news conference.
"I'm not complaining for the players that are not available. It'll be a difficult game, but I don't think it's an easy game for City. They have better quality than us, but I'm sure they will have a difficult game.
Gundogan scored four goals and provided one assist in five appearances as Pep Guardiola's side won each of their six league games to continue their march towards the Premier League title.
"I am very proud to win this award again - but I am most proud of being part of this amazing team," Gundogan, 30, said.
Spaniard Guardiola spent trophy-laden seasons with Barcelona and Bayern Munich before joining City ahead of the 2016-17 season and has since guided them to two league titles, three League Cups and the FA Cup.
"I had incredibly hungry teams in my career, lucky to be together in Barcelona and Bayern. To do what we've done in these four years, still winning ... these guys have something special," Guardiola told reporters.
Goalkeeper Alisson was granted compassionate leave following the sudden death of his father last week and subsequently missed the 2-0 win over Sheffield United on Sunday.
"So Ali trained now for the full week and yes we should expect that he is able to return," Klopp told a news conference on Wednesday.
City took the lead in the 30th minute with central defender Ruben Dias heading in a Kevin De Bruyne cross, but the Hammers drew level through Michail Antonio two minutes before the interval.
Pep Guardiola's side secured their 14th consecutive league win, however, when Dias' fellow defender John Stones slotted home after being picked out by a Riyad Mahrez pull back.
Saturday's 3-1 defeat at Leicester City left Liverpool in fourth, 13 points behind leaders Manchester City having played a game more, and led to rumours that Klopp could walk away from the club.
I am grateful for the support. But fans can think about other things, nobody needs to worry.
Garcia, 20, came through Barca's academy before leaving for City in 2017 but has run down his contract and has not featured for Pep Guardiola's side in the Premier League since late November.
I'm sure he'll come for next season and if it's not possible in January then we'll accept that and move on.
The hastily negotiated Brexit deal could have unprecedented consequences for football clubs, in terms of the scouting, recruiting and development of young talent.
Manchester City, under the ownership of Sheikh Mansour and the City Football Group (CFG), have unlocked the solution to these regulatory challenges.