Chelsea have lodged an official complaint with European soccer's governing body UEFA after up to 50 of their fans possessing tickets were stopped from entering the ground for Tuesday's Champions League game at CSKA Moscow.
The supporters involved missed most of the first half of the 1-0 victory over CSKA, said Chelsea on their official website.
Dutch winger Arjen Robben scored the only goal in the 24th
minute as the London club qualified for the knockout round of the Champions League with two matches still to play.
Chelsea have collected a maximum 12 points from four matches in Group H, eight ahead of CSKA and Paris St Germain, who held champions Porto to a 0-0 draw in Portugal on Tuesday.