Chelsea qualified for the knockout stages of the Champions League despite losing 1-0 to Basel on Tuesday after a late strike by Mohamed Salah gave the Swiss side a deserved victory.
Chelsea has nine points in Group E, followed by Basel on eight and Schalke with seven - after the German side was held to a 0-0 draw at Steaua Bucharest on Tuesday.
But the fact that Basel travels to Schalke in the final round of matches means that only one of those clubs can overhaul Jose Mourinho's group leaders.
Chelsea appeared to come to Switzerland looking for a draw that would clinch its last-16 place, and failed to register a single goal attempt before the Egypt forward's well-earned goal.
Salah sprinted clear of Chelsea's defense to clip a left-foot shot over the advancing Petr Cech and complete home and away wins for the Swiss team against the 2012 European champion.
English opposition again brought the best from Basel, which eliminated Manchester United from the group stage two years ago and beat Chelsea 2-1 in September.
Cech had kept three clean sheets in the competition since that surprising win at Stamford Bridge and looked unbeatable as Basel had six first-half shots on target.
In the third minute Cech crouched to push out a curling free-kick crossed from the left by Taulant Xhaka.
Within a three-minute spell, Cech dived and leaped to tip away 20-meter (-yard) shots by Fabian Frei and Salah, respectively.
Cech's best save denied Salah in the 24th, reaching back with his left hand as he fell to his knees to push the swerving ball up and over the crossbar.
Basel also had two penalty appeals rejected before the break, for an accidental handball by Frank Lampard and left-back Cesar Azpilicueta's timely challenge as Salah shaped to shoot.
Chelsea was livelier in the second half thanks to substitutes Eden Hazard and Fernando Torres, who replaced the injured Samuel Eto'o just before half time, but still failed to create a scoring chance.
Basel lifted the pace in the closing minutes and midfielder Geoffroy Serey Die fired a volley from 25 meters (yards) skidding just beyond Cech's right post.
Defender Fabian Schaer tried his luck from further out in the 85th and forced Cech to dive low to his left to smother the ball.
Schaer then delivered a perfect 60-meter diagonal pass into Salah's stride for the decisive goal as the Egyptian left Chelsea right-back Branislav Ivanovic trailing.
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