AC Milan players walked off the pitch due to alleged racist chants from Udinese fans towards goalkeeper Mike Maignan.
Play was suspended for around 10 minutes at Udinese's Bluenergy Stadium following the alleged incident during the first half.
"There is absolutely no place in our game for racism: we are appalled. We are with you, Mike," AC Milan said in a post on X, formerly Twitter, following the incident.
City rivals Inter Milan shared their support, replying to the post: "We are brothers of the world, against all forms of discrimination. By your side."
The Serie A League added that it "condemns all forms of racism".
Maignan, 28, who was born in French Guiana but grew up in Paris and plays for the French national team, was seen remonstrating with referee Fabio Maresca before taking off his gloves and walking off.
As he walked down the tunnel leading off the pitch, he was followed by his teammates.
He had also told the referee about alleged monkey chants earlier in the match, prompting an announcement in the stadium asking fans to stop.
"They made monkey noises and it's not the first time it's happened to me," the Maignan told DAZN after the game.
The incident took place around 30 minutes into the match, shortly after former Chelsea midfielder Ruben Loftus-Cheek had given Milan the lead with a low first-time shot inside the post.
Paris Saint-Germain forward Kylian Mbappe and England's Ian Wright later showed support for Maignan with the former writing: "You are very far from being alone Mike Maignan. We are all with you. Still the same problems and still NO solution. Enough is enough !!!!!!!!!!!! NO TO RACISM."
Former Arsenal forward Wright added: "Solidarity from the rest of the team. Keep walking off!! We did 'playing through it' and nothing has changed. Points deductions needed, the fines are pointless."
Minutes after the restart, Udinese equalised through Lazar Samardzic, before former Newcastle player Florian Thauvin scored to give the home side the lead.
However, Milan striker Luka Jovic scored late to draw the game level, before Noah Okafor struck in injury time to secure a 3-2 win for the visitors.
The incident comes after Belgium international Romelu Lukaku was sent off after being racially abused while playing for Inter Milan in April last year.
The Belgium forward was shown a second yellow card for his celebration - putting his finger to his lips in a shushing gesture - in front of the home fans after converting a stoppage-time penalty to earn Inter a 1-1 draw in Turin.
Lukaku's then agents claimed the striker was racially abused by Juventus fans, before, during, and after the penalty and called on the club to apologise.
Police said 171 fans had been given stadium bans following the incident, while Juventus were hit with a one game partial stadium closure by Italy's top league, Serie A.