The incident took place during a UEFA Youth League match between the two clubs in Russia. Brewster had to be held back by teammates after Spartak defender Leonid Mironov allegedly made racist comments towards him.
Five players from each team and two match officials were interviewed by the UEFA ethics committee, but the allegation was not corroborated. Therefore, UEFA dropped the charges on Mironov and Spartak.
A statement released by UEFA mentioned that they understood Brewster's accusations were made in "good faith".
The statement read: "The inspector took statements from five players from both teams, as well as from two match officials, who were in the vicinity of the alleged incident. None of these heard any discriminatory words.
"Mironov was also interviewed by the inspector and stated that he indeed swore at Rhian Brewster, but he unreservedly denied using any discriminatory language.
"After concluding his investigation, the inspector found no evidence to corroborate the allegations, which he believed were made in complete good faith by Brewster.
"Therefore, the UEFA Control, Ethics and Disciplinary Body, following the recommendation of the inspector, established that there was no evidence that would legally support sanctioning the FC Spartak Moskva youth player Mironov and thus decided to close the disciplinary proceedings."