Leeds United said social media threats aimed at striker Patrick Bamford and his family after he missed a penalty in their 2-2 draw with Newcastle United on Saturday were unacceptable.
Bamford's spot kick was saved by Nick Pope in the first half of the Premier League game after Joelinton had bundled over Junior Firpo in the box.
"Overnight Patrick Bamford and his family have received completely unacceptable online abuse including several threats via Twitter," Leeds said on Sunday. "The time for this behaviour to stop is now."
Leeds, who are in the relegation zone at 18th spot, travel to West Ham United before hosting Tottenham Hotspur in their final game of the season.