United were thumped 4-0 at Falmer stadium.
Shearer said: "They were shambolic, Manchester United, they were an embarrassment.
"And if he hasn't already, Ralf Rangnick should get his players in tomorrow and show them the performance from Brighton.
“Because this is what committed footballers do for their club, their fans, for their teammates and their managers. They work hard, they are prepared to put a shift in, they are organised and they are committed. It should be a given, but it's not at Manchester United.
“They should watch this, because these Brighton players today showed what they should do for their fans. They were magnificent, and some of the football they played was fantastic. They [United] are totally lost, but what are they doing on the training ground?
“You have to work on things, and that's what Brighton do. United were an embarrassment to their football club today."
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