The head-to-head rule which UEFA use to separate teams who are level on points means that all sorts of complex connotations are possible as the three sides bid to follow runaway Group E leaders Bayern Munich into the next round.
Manchester City have never won a competitive match in Italy in four previous attempts and, even if they break that taboo, could still suffer another premature group stage exit.
Roma's fate is in their own hands as a win will be enough for them while a draw, paradoxically, could send either themselves or City through, depending on CSKA's performance.
"City are obliged to win. They have all the pressure. Not Roma. City are in the same period that Chelsea used to be before they won it. It becomes complex until you win the trophy," Roma's Ivorian striker Gervinho told British media.
Roma, City and CSKA all have five points from five games after mediocre campaigns in a group dominated by Bayern.
A win for Roma, still in the hunt despite losing 7-1 at home to the Bavarians, will guarantee them a second place finish, even if CSKA also win, as the Serie A side would have the better head-to-head record against the Russians.
CSKA can only qualify if they win in Munich and Roma fail to beat City while City will qualify if they win and CSKA do not.
The rule fun begins if Roma and City draw. If CSKA also draw, Roma would go through, and if the Russians lose, it would come down to the head-to-head record between the Serie A and English side. A goalless draw would favour Roma and a score draw would do for City.
City have gone out in the group stage twice in three attempts and their task has been made ever harder after their leading scorer Sergio Aguero was injured against Everton on Saturday, forcing him out of the tie.
City will also be without midfielder Yaya Toure who is suspended, while skipper Vincent Kompany, and midfielders Stefan Jovetic and Fernandinho face late fitness tests.
However, forward James Milner believes that even without Aguero and Toure City can get the result they need.
"Sergio is a world class player, and has been outstanding all season so the injury has come at a bad time.
"He is going to be very difficult to replace and even without him and Yaya (Toure) we have a fantastic squad of players and, with the players, we have I am not too worried."
"We've had to win our last two games to qualify
and I believe we can win in Rome after beating Bayern."
(Additional reporting by Mike Collett, Editing by Brian Homewood)
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