The American sportswear giants posted an image on their Instagram account similar to the one of American footballer Colin Kaepernick.
Sterling was subject of alleged racist abuse at Chelsea last weekend, and hit back in an Instagram post.
The Man City forward called for "fair publicity" and giving "all players an equal chance", and Nike have backed him.
Nike's Instagram post read: "Speaking up doesn't always make life easier. But easy never changed anything".
The close-up black and white image of Sterling's face resembles the one used in Nike's 'Just Do It' campaign featuring Kaepernick.
That Kaepernick advert that was released in September read: "Believe in something, even if it means sacrificing everything."
The 31-year-old took a knee during the US national anthem ahead of a pre-season NFL game in 2016 when he was playing for the San Francisco 49ers.
Kaepernick was speaking out against social injustice and police brutality in America, and many more black athletes have since performed similar protests.
The quarterback left the 49ers after the 2016 season and is still without a team.
He has since filed a grievance against the NFL, accusing team owners of collusion to keep him away from the league.
America's most prominent athlete LeBron James backed the advert, saying: "I stand with Nike, all day, every day."
Sterling came off the bench to score Man City's third goal in a 3-1 victory against Everton at the Etihad on Saturday.
City boss Pep Guardiola paid tribute to Sterling and the way he has handled himself this week.
Guardiola said: "My feeling is he has handled many situations in the last year.
"There are many rumours that people have been talking about, and not nice things about him or his family or, in this case, the colour of his skin.
"And that is why I admire him. I admire that it is not easy for him but he is calm, he is happy playing football and he is beloved.
"He is incredible for all the staff, locker room and his team-mates. It is good. Hopefully we can improve on that and move forward."
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