UEFA imposed the 'improper conduct' sanction after three flares were seen in Section 111 at Parkhead - which houses supporters' group the Green Brigade - during the match with Cliftonville on July 23.
The incidents forced Celtic to write to season ticket holders in the area warning the section could be closed down if a repeat of the behaviour was noted.
Celtic beat the Irish champions 5-0 on aggregate and subsequent victories over Elfsborg and Shakhter Karagandy saw them joined by Barcelona, AC Milan and Ajax in the group stages.
The sanction comes 20 months after Celtic were fined 25,000 euros over the conduct of their fans during a Europa League tie against Udinese in Italy.
Following the 1-1 draw at the Stadio Friuli in December 2011, the Scottish champions were charged with the 'displaying of a banner of an offensive nature and the setting off of fireworks by supporters'.