Former Premier League ref Keith Hackett says Chelsea defender David Luiz should've been sent off against Manchester United.

United succumbed to a humiliating 4-0 defeat at Stamford Bridge after goals from Pedro, Gary Cahill, Eden Hazard and N'Golo Kante.

But the scoreline might have had a different look to it if Luiz had been sent off for a foul on Marouane Fellaini five minutes before the break with the score at 2-0 to the Blues.

Hackett told the Telegraph: "At Stamford Bridge on Sunday Martin Atkinson lacked the courage to send David Luiz off.

"A red card offence is a tackle that is reckless with excessive force that endangers the safety of an opponent, and Luiz's challenge on Marouane Fellaini during Chelsea's 4-0 win over Manchester United was all three of those.

"Martin needed to be 100% certain to make the call, but from where he was standing I cannot see how he could have had any doubt.

"You have to be brave enough in the big games to make the correct calls on the big decisions, and Martin wasn't.

"It doesn't matter that this was a home player in front of a passionate crowd, that cannot worry you as a referee.

"Ultimately you have to remember the mantra that 'this is the law, and I'm the person who has to carry out the law'."