Rangers defender Connor Goldson claimed he was struck by objects thrown from the crowd during the club's Europa League draw in Porto.
The centre-half also said goalscorer Alfredo Morelos was hit in the 1-1 stalemate at the Estadio do Dragao.
Asked after the game, manager Steven Gerrard told the media he was unaware of any incidents.
"There was a lot of lighters and coins thrown. I got hit. Buff [Morelos] got hit as well," said Goldson.
"Then the referee told me to stop [celebrating] and walk away and I just picked up the lighter and coin and told him, but nothing got done.
"It's crazy. I can understand having a passion for your team but at the same time they have come to watch us as athletes trying to do our best for our own team, and I don't think that's acceptable."