Brewster had just helped the Reds record a 2-0 win over their Russian opponents when he had to be restrained by teammates and coaching staff after allegedly being on the receiving end of comments from one of the visiting team.
Boss Steven Gerrard is quoted by The Sun as saying: "It's difficult for me to comment on it right now. It's something that the club will look into and deal with.
"I'd rather talk about Rhian Brewster's performance. I don't want to take any gloss off that because he was superb."
Brewster has hit the headlines in recent months after helping England win the Under-17 World Cup in India.
The two clubs meet in the Champions League on Wednesday night with Liverpool requiring a result to secure progress through to the last 16 of the competition.