Southampton involve police after Walker-Peters racial abuse
Walker-Peters was targeted online after his challenge on United's 18-year-old Alejandro Garnacho left the winger in pain, forcing manager Erik ten Hag into withdrawing his second-half substitute.
Garnacho, who has four goals and four assists this season, later left Old Trafford on crutches with Ten Hag confirming he had twisted his ankle.
"In February 2021 the club made a statement about one of our young players receiving abhorrent racial abuse following a match against Manchester United," Southampton said.
"More than two years on, we find ourselves in the exact same position: disgusted and disappointed in the behaviour of those online who lower themselves to abusing players for the colour of their skin.
"What is equally frustrating is the lack of meaningful action in those two years from the social media platforms who allow such hatred to breed and fester."
Saints said the messages have been forwarded to Hampshire Police while they have also reported the posts to the social media platforms.
"We can only hope that they finally pay attention to what continues to be a major problem and that we do not find ourselves repeating these words in another two years time," the club added.