Jose Mourinho, the United manager, suffered his heaviest league defeat in English football on his first visit to Stamford Bridge since being dismissed by Chelsea last December.
Despite the chastening reverse, several members of his side chatted and joked with their opponents after their defeat was confirmed.
Giggs, United’s record appearance holder and the club’s assistant manager under Louis van Gaal last season, castigated the players for their post-match behaviour.
“You can get beat in a football match, but then when you’re getting beat and you’re swapping shirts – which is something I don’t like, call me old fashioned,” he said.
“If you get beat 4-0, you congratulate the opposition, you thank the supporters and then you get off the pitch.
“You don’t stand around on the pitch, swapping shirts and laughing, with the team that’s just beat you.”
United fell behind after just 30 seconds at Stamford Bridge, with Pedro capitalising on Chris Smalling and Daley Blind’s defensive mix-up to put the hosts ahead.
Gary Cahill added a second from a corner, before Eden Hazard and N’Golo Kante’s second-half strikes rounded off an emphatic Chelsea win.
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