The incidents occurred during the 5-1 defeat at Real Madrid on Oct. 18.
European soccer's ruling body UEFA added that the Polish team's fans were also provisionally banned for two more away matches in European competition, deferring that additional sanction for a probationary period of one year.
Legia supporters were involved in clashes with police outside the Bernabeu stadium last month and the reverse fixture on Nov. 2 was played behind closed doors because of previous crowd disturbances.
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It was the fourth time they had to play behind closed doors in Europe following three punishments in the Europa League since 2013.
Legia are bottom of Champions League Group F with one point from four matches, nine points behind leaders Dortmund.
(Reporting by Julien Pretot; Editing by Tony Jimenez)
