Since he was closest to Fred, he could have gone over and put his arm around him, or patted him on the back, to show some solidarity. Like a few of the other City players did, when they came over.
Fred said he himself didn't even notice the racism before after the game, and he was both the closest person and the guy the abuse was directed at.
Sterling, for his awful crime of shining light on an inconvenient and uncomfortable part of football and society in general, is supposed to be some sort of anti-racist superhero. He needs to, during a game, be hyper focused on noticing sounds and gestures from the stands, and he needs to call out any and all incidents personally. If he doesn't, well, he's just not committed to the cause, he's in it for himself, for attention, or whatever.
This attitude towards Sterling (yours is a pretty mild example, just the latest one I read) all over this thread is so disappointing. It's downplaying the racism in this specific incident by taking the focus off of the abuse and on to Sterling, and it's downplaying the issue of racism in general.
Why is this post full of people talking about Sterling? Because he's black, and because he has talked about racism before. That's it, and it's ridiculous. Placing the burden of fighting anti-black racism on black people is a tradition as old as the racism itself, and it's so so wrong on every level.