Chelsea defender Marcos Alonso's apparent stamp on Southampton striker Shane Long is under FA investigation, Sky Sports News understands.
Saints manager Mark Hughes accused Alonso of almost breaking Long's leg in the challenge, which happened when Chelsea were 1-0 down.
Referee Mike Dean did not book Alonso for the incident, which happened directly in front of fourth official Roger East.
Chelsea came from behind to win 3-2, leaving Southampton five points off safety in the Premier League.
Hughes urged the FA to look at it retrospectively.
"Shane's got a gash down the calf, having seen it again there's a clear red card," he said after the game. "There's clear intent to hurt Shane, it was raked down the back of the calf.
"It's a dangerous tackle and could have broken his leg, in my view, and how the three officials who were near it all missed it was a mystery to me."
Sky Sports pundits Matt Le Tissier and Dennis Wise called Dean's decision "embarrassing", while former referee Dermot Gallagher said he expected the Football Association to revisit the incident.