The 28-year-old had scored a 60th-minute winner for Porto against his former club which sparked the home fans to aim even more vitriol at the France-born player which had started as early as the pre-match warm-up.
In the 71st minute, Marega signalled to the bench that he was walking off in protest even though team-mates, Porto coach Sergio Conceiçao and Vitoria players tried to get him to stay on the pitch.
As he walked off, an angry and upset Marega gave a thumbs-down signal with both gloved hands to the home fans.
He had already been given a yellow card for his goal celebration.
Marega played for Vitoria Guimaraes from 2016-2017 on loan from Porto, scoring 13 goals in 25 games.
Marega later wrote on Instagram after the game, which Porto won 2-1, that his tormentors were "idiots who come to the stadium just to make racist chants."