Two defeats in three league matches have cut short Carlo Ancelotti's honeymoon period as Chelsea coach but his concerns pale into insignificance alongside those of Atletico Madrid counterpart Abel Resino.
Saturday's 2-1 reverse at Aston Villa left Chelsea trailing Manchester United by one point at the top of the Premier League and captain John Terry stamping his feet in disapproval as the second Villa goal went in.
It hardly represented a crisis and victory over Atletico at Stamford Bridge on Wednesday will virtually assure Chelsea a place in the knockout round of the Champions League.
Resino's Atletico though are having a torrid time and a game at Chelsea, who are unbeaten in 19 home Champions League ties, is hardly the easiest task to try and reverse the slump.
Sunday's 3-0 defeat by Osasuna was their third defeat in seven league games and they are a distant 15th in La Liga.
“The football gods are being very unfair to us,” Resino said. “We had a lot of chances but that's what happens when you are on a bad run, the ball just won't go in the net.”
Defeat by Porto in their last Champions League outing also left Atletico at the bottom of Group D with one point. If they suffer another reverse in London their hopes of progressing will be fading fast.
Brazilian midfielder Cleber Santana says the Chelsea clash is coming at a key moment for the club as they seek to turn their faltering season around. “We are facing a very difficult encounter and we have to be at the top of our game,” he said. “It's a vital match for us.”
Atletico will have Diego Forlan back after the Uruguay striker missed the Osasuna defeat because of fatigue and a muscle problem following his midweek international exploits.
Chelsea will again be without Didier Drogba, who is completing his European ban for his behaviour in the semi-final defeat by Barcelona last season. The loss of the striker has been negated by the form of Nicolas Anelka who has scored in both their Champions League victories this season.
Red Devils face CSKA
Manchester United return to the scene of their 2008 Champions League final victory over Chelsea looking for a win over CSKA Moscow that will virtually ensure their passage to the knockout stages of this season's competition.
Despite some mixed displays in the Premier League this season, the English champions have looked assured on the European stage so far, recording wins over Besiktas, in Turkey, and German champions Wolfsburg at Old Trafford.
Another three points at the Luzhniki Stadium — where John Terry's slip and penalty miss in the decisive shootout effectively gifted United the third European Cup triumph in the club's history — would put Sir Alex Ferguson's side firmly in control of group B.
History, however, suggests that will not be a straightforward affair. United have never won in Russia while CSKA have won their last six European ties at home.
CSKA were far from impressive in a 1-1 draw at minnows Nalchik in the Russian league at the weekend and will be missing Marc Gonzalez, who suffered a serious ankle injury on international duty with Chile last week, while Brazilian striker Guilherme is a major doubt.
United's absentees are more significant with Wayne Rooney, who is still struggling to recover from a calf problem, and Ryan Giggs, who has been outstanding this season, both left at home in order to ensure they are fully rested for Sunday's Premier League showdown with Liverpool at Anfield.
South Korean midfielder Park Ji-Sung, Scotland captain Darren Fletcher and France left-back Patrice Evra have also missed the trip through injury.
But Ferguson has Nemanja Vidic, once a star with CSKA's great rivals Spartak Moscow, back from injury and could opt to pair the Serbia centreback with Jonny Evans at the expense of Rio Ferdinand.