"Honestly, it makes me feel sick, coming in seeing Axel the next day after the game.
"But I feel like it's an absolute shambles and that's somebody, one of my brothers who I've grown up with for a long, long time now, and to see that happen to him is absolutely disgusting."
Several Premier League players have been subject to racist abuse on social media over the past fortnight and McTominay cannot understand why someone's race and ethnicity should be mentioned.
"I just don't even think about the situation with people having different ethnic backgrounds," he said. "I just never would say, 'I'm white, Axel's black.' How are we any different? It's exactly the same.
"We've grown up through the same school together. We've played football together for years. So, it infuriates me.
"But I feel like now we are getting to the awareness which it needs to have, because these are my brothers who I've played with for years and years, and to see it happening is a shambles. It's a disgrace."
The Premier League's online abuse reporting system is helping players, managers and their family members who receive serious discriminatory online abuse. Each case is rapidly reviewed, reported to the relevant social media company, investigated and, where appropriate, legal action is taken.
The League and clubs are also encouraging fans to play their part in the fight against racism by reporting it whenever they encounter it.
See: How to report racism
Last month, the Premier League launched its No Room For Racism Action Plan, outlining a series of commitments aimed at creating greater access to opportunities and career progression for Black, Asian and other minority ethnic groups in football, and actions to eradicate racial prejudice.
As part of its No Room For Racism initiative to help educate about diversity, inclusion and racism, the League has also produced free learning resources in the Premier League Primary Stars programme for schools and families.