Simple. Both Manchester clubs and Tottenham are the winners of their groups and the Blues' can't play them in the last 16-stage because clubs from the same country can't face each other in the upcoming stage of the competition.
Diego Perotti scored early in the second-half as Roma edged Qarabag 1-0 at the Stadio Olympico to win Group C ahead of Chelsea, who had to come from behind to draw 1-1 at home to Atletico.
Chelsea were already through to the knockout stages, but blew their chance to finish in first place and in theory earn an easier draw.
That is bad news for Antonio Conte's side, who could be pitted against Champions League heavyweights including Barcelona and Paris Saint-Germain in next week's last 16 draw. Here are who they could face in the last 16. We know PSG and Barcelona are very good but we are Chelsea so we have to be ready for everything. We created many chances to score.
Next Up: Chelsea travel to West Ham on Saturday.
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He also made it clear that while the draw options were less than ideal, Chelsea are a big enough club to be able to cope with whatever is thrown at them.
Hazard said: "It's not a problem".
Chelsea then enjoyed a purple patch with Andreas Christensen heading straight at Oblak before Hazard's shot was deflected over the bar and Morata's header was kept out by the Atletico goalkeeper.
As it stands, Turkish side Besiktas are the only other possible opponents for the Blues in the knockout stages.
But Saul Niguez escaped the attentions of Tiemoue Bakayoko to plant home a header from Fernando Torres' near-post flick-on after 56 minutes.
Christensen should have equalised from a Cesc Fabregas cross 10 minutes later, but the Chelsea defender somehow headed wide of the open goal.