Manchester United manager Ole Gunnar Solskjaer said he was "lost for words" after Marcus Rashford suffered racist abuse on social media on Saturday.
Rashford missed a second-half penalty as United suffered a shock 2-1 defeat to Crystal Palace at Old Trafford - their first loss of the new season.
The Red Devils were trailing to Jordan Ayew's first-half effort when Rashford smashed a spot-kick off the inside of the left-hand post, just five days after Paul Pogba had missed from 12 yards in the 1-1 draw with Wolves.
Pogba was subjected to vile social media abuse after that miss and there were similar posts targeting Rashford after the Palace game.
Solskjaer called on companies such as Twitter to do more to stop abusers "hiding behind fake identities" after Pogba was targeted, and he has again called for action to be taken.
Speaking after the match, Solskjaer said: "It's the same as we spoke about before the weekend: it's unheard of and it needs to stop.
"I'm lost for words. We keep having all these campaigns, and they keep hiding behind fake identities. It's just crazy that we talk about this in 2019."
The abuse was condemned by anti-discrimination body Kick It Out, who tweeted: "This problem will not go away and needs decisive action - that's what we'll be making clear to Twitter when we meet."
United levelled late on through Daniel James only for Patrick van Aanholt to snatch a winner in the third minute of injury time.
Solskjaer's side next face Southampton away from home next Saturday.
