Here are Chelsea’s worst case scenarios:
Chelsea
Barcelona
Napoli
RB Leipzig
Because Chelsea are in Pot 1 they will avoid the likes of current holders Real Madrid and last season's runners-up Juventus.
Chelsea
PSG
Roma
Feyenoord
However, they will draw a team from the dangerous Pot 2 which includes the likes of Barcelona, Atletico Madrid, PSG and Borussia Dortmund.
Chelsea
Atletico Madrid
Besiktas
Sporting
RB Leipzig are the toughest looking opponents in Pot 4, although Chelsea could also face Dutch champions Feyenoord or Portuguese side Sporting.
http://www.independent.co.uk/sport/football/european/champions-league-draw-chelsea-group-worst-opponents-barcelona-atletico-madrid-psg-dortmund-napoli-a7907296.html