When Manchester City slumped to a 2-1 home defeat at the hands of CSKA Moscow few people gave them a chance of progressing from the group stages of the Champions League.
The result left the Premier League champions with just two points from their opening four fixtures, and with games against Bayern Munich and Roma to follow, Manuel Pellegrini's side looked doomed.
However, Sergio Aguero hadn't given up hope and it was his hat-trick against Bayern that sealed a famous 3-2 win and set up tonight's crucial tie.
The equation is far from simple for City; even a win in Rome wouldn't be enough to qualify should CSKA take three points from their trip to Munich.
But, that said, Pellegrini's men could qualify with a score draw should Bayern defeat the Russians, although a 0-0 stalemate would see them eliminated.
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The only simple fact from a City point of view is this; they must score if they're to progress, and their attempts to do so will be hugely hindered by the absence of the injured Aguero.
That City are still in with a chance of qualifying is largely down to Aguero, who's aforementioned hat-trick took his tally to five Champions League goals this campaign.
Disaster struck for the Argentine at the weekend though when he limped off after just two minutes of the weekend clash with Everton.
The strikers teary exit suggested the injury was serious, and Pellegrini has since confirmed his star man could miss up to six weeks.
In his absence the fit again Edin Dzeko is likely to lead the line, though he could be kept on the bench with Stevan Jovetic having returned to training following a hamstring complaint.
Jovetic is not the only City star to have given Pellegrini a boost this week, with David Silva and Vincent Kompany also taking part in training on Tuesday after knee and hamstring problems respectively.
The duo will both face late fitness tests ahead of the game, with Vincent Kompany all but certain to start should he satisfy the medical staff, while Silva's place in the starting 11 is far from guaranteed regardless of the outcome of his assessment.
The Belgian defender has been the rock upon which City's success has been built in recent years and deputies Martin Demichelis and Eliaquim Mangala have been far from convincing in his absence.
In Daniele De Ross, Roma boast a central midfielder who has long been coveted by City, among other top Premier League teams, and Pellegrini's side will have to be at their best to dominate him in the middle of the park.
That task is made harder by the continued suspension of Yaya Toure who's still missing following his silly red card against CSKA.
Fernandinho is available following a niggle and is likely to be joined by Frank Lampard after the Englishman's composed display in the 3-2 win against Bayern.
A key decision for Pellegrini will be whether to attempt to over-run Roma's midfield by deploying a central five, or to go all out for the win and go with two wide men and a front two.
Hart; Zabaleta, Kompany, Demichelis, Clichy; Milner, Lampard, Fernando, Fernandinho, Nasri; Dzeko
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