UEFA is set to investigate after a firecracker was apparently set off among Portugal's supporters during their 1-1 draw with Iceland at Euro 2016 on Tuesday.
Nani opened the scoring for Fernando Santos' men in the 31st minute in Saint-Etienne, but they were pegged back early in the second half.
The governing body confirmed to Omnisport it would investigate the apparent firecracker used after Nani's opener.
It continues a troublesome tournament, at which Russia have been given a suspended disqualification after clashes with England fans.
Birkir Bjarnason scored a second-half goal for Iceland as the minnows surprisingly held Portugal in the Group F clash.