Tottenham could be in trouble with UEFA after Dinamo Zagreb fans lit flares at the away end of White Hart Lane.
Supporters of the Croatian league leaders clashed with stewards and fans in the first half of the UEFA Cup defeat to Spurs, and there were five arrests for public-order offences on the night.
UEFA, Europe's governing body, will wait for the report of the match delegate before deciding if Spurs will be punished, with a fine being most likely if they take action.
The Football Association, meanwhile, are looking at recent incidents involving Spurs fans during domestic games, including the abuse Portsmouth defender Sol Campbell suffered when he faced his former club.
Spurs issued a statement on their website ahead of the Dinamo game, warning how the club are under the spotlight after a coin-throwing incident during the defeat at Stoke.
After the last-gasp draw against rivals Arsenal at the Emirates Stadium, a number of fans also ran onto the pitch to celebrate the 4-4 results.
"As a result of both of these incidents, we are now the subject of investigations by the Football Association," read the statement from Spurs.
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