Earlier on Thursday, Blues boss Roberto Mancini had expressed hope the pair would be allowed to join the Ivory Coast squad for this month's African Nations Cup slightly later than planned, which would allow them to feature in the third-round match at the Etihad Stadium.
Mancini said he expected to learn within 24 hours whether the Toure brothers - defender Kolo and midfielder Yaya - would be excused a planned squad gathering in Paris on Saturday before they fly to Abu Dhabi for a two-week training camp.
The answer came a lot sooner than that, with Ivory Coast coach Francois Zahoui responding negatively.
"Clubs know the rules," Zahoui told BBC Africa. "I'm expecting them [the Toures] for the FIFA deadline."
FIFA give countries the right to call up players a fortnight before the tournament begins, and the African Nations Cup starts on January 21.
City had been unaware that was an official position that could not be changed.
However, following further discussions, they have now accepted that the Toure brothers will have to be in France on Saturday, and thus will miss the United game, both legs of the Carling Cup semi-final with Liverpool later this month and up to five Premier League matches, depending upon how far the Ivory Coast progress.
It is a major blow for City, whose manager has revealed he may struggle to fill his bench on Sunday.
Gareth Barry is suspended, Owen Hargreaves is not considered fit enough to be involved, and Mario Balotelli is troubled by an ankle injury that prevented him playing against both Sunderland and Liverpool.
"We have 17 players," said Mancini.
"I do not know how it is going to work.
"I always said we could have a problem in January. Yaya is an important player for us.
"Kolo is different. We have eight defenders and if we are lucky, we don't have any injuries.
"In midfield we have a big problem. On Sunday we only have James Milner and Nigel de Jong available."
Mancini does have the option of pushing Pablo Zabaleta into a central area, and also Samir Nasri if the former Arsenal man recovers from illness.
Meanwhile, City officials have distanced themselves from reports that both QPR and Wolves have lodged bids for Nedum Onuoha.
However, it does appear Carlos Tevez will be moving on amid reports he has opened negotiations with Inter Milan.
Mancini said: "I do not know the situation today but I do hope for him he can close a deal with a team this week because he hasn't played for three months."