Rio Ferdinand described Alexandre J ankewitz's red card horror tackle on Scott McTominay as 'crazy'.
The Southampton youngster was sent off just over 70 seconds into the 9-0 drubbing for a high foot that caught McTominay on the thigh.
Jankewitz is the fourth player in Premier League history to be sent off in the opening two minutes of a game. His challenge left McTominay with clear stud marks on his leg.
McTominay was able to continue and scored United's sixth goal of the game in the second half.
Saints boss Ralph Hasenhuttl appeared furious at the tackle, which reduced his already injury-depleted side to 10 men and allowed United to run riot, going into half-time 4-0 up.
Speaking on BT Sport, Ferdinand said he doubted Hasenhuttl would need to give Jankewitz a dressing down over the tackle due to how clearly bad it was.
Yet the former United defender warned that, had McTominay's leg not been in the air, it could well have left the midfielder with a bad break.
Ferdinand said: "It was a crazy tackle to start the game off and it killed everything we thought was going to happen in the game.
"It’s such a bad tackle, when I saw it the first time, I thought it was bad, but when you see the replays, it’s a terrible tackle.
"I don’t think the manager will need to tell him anything in the changing room, I don’t think he needs to go mad.
"If his leg was planted then you’d think it’s a leg-breaker."
