The forward from Mali, 28, scored what proved to be the winning strike in the 60th minute and celebrated the goal by pointing to his skin in response to a section of home fans who targeted him by making monkey noises during the league match on Sunday.
He was shown a yellow card for the reaction and after the abuse continued he tried to leave the pitch, pointing his thumbs down to the crowd, but was restrained by his teammates for several minutes.
Porto coach Sergio Conceicao, who also went on the field and spoke with Marega, was eventually forced to substitute the Malian player in the 72nd minute.
“We are completely indignant,” Conceicao told reporters.
“They insulted Marega since the warm up. We are all a family here, regardless of our nationality, skin colour, height or the colour of our hair and we all deserve respect. What happened here is outrageous.
“I know the fans here are very passionate about their club and many fans are not represented by some of the people who were in the crowd today.”
— VSPORTS (@vsports_pt) February 16, 2020
Marega later posted a message on his Instagram page calling the supporters who targeted him “idiots” and also criticising the match officials.
“And I also thank the referees for not defending me and for giving me a yellow card because I defend my skin color,” he wrote. “I hope I never see you on a football field again! YOU ARE A SHAME !!!!”
The league’s organising body Liga Portugal condemned the chants.
“Liga Portugal does not agree and never will with acts of racism, xenophobia or intolerance that jeopardise the dignity of footballers or any human beings,” said a statement on its website.
“Liga Portugal will do everything to ensure that this episode and all other racist incidents do not go unpunished.
“We believe this is a fight where your team’s colours do not matter and everyone must come together to eradicate this scourge on the game.”
FC Porto striker Moussa Marega tried to walk off the pitch after being racially abused by some Vitoria SC fans tonight.
— Goal (@goal) February 16, 2020
Portuguese newspaper A Bola reported no Porto players spoke to the media after the game in solidarity with Marega.
Vitoria Guimaraes said it would investigate the incident.
“[The club] will not fail to censor any and all manifestations of violence, racism or intolerance,” it said.
Porto are second in Portugal’s top division, trailing behind leaders Benfica by a point after 21 games.
Racism remains rife in international football, with fans often taking aim at opposing team’s players.
In January, an Italian Serie A match between home side Brescia and Lazio was briefly halted after striker Mario Boletelli was targeted by racist and other offensive chants by visiting fans.
Last October, Bulgarian fans taunted England’s black players with Nazi salutes and monkey chants during a Euro 2020 qualifier in Sofia, prompting match officials to halt the game twice.