Manchester United's players took refuge on the floor of the coach after it was held up near the stadium by chanting fans who hurled dozens of missiles and let off smoke bombs, as mounted police tried to keep order.
The bus was left with gaping holes in the protective glass covering its windows in the ugly scenes, which held up kick-off for 45 minutes on Tuesday.
The incident carried echoes of England's notorious hooliganism of the 1980s and overshadowed the final game after 112 years at the Boleyn Ground, also known as Upton Park.
The Football Association and police both said they would investigate. During the game, won 3-2 by West Ham, Manchester United goalkeeper David de Gea appeared to have bottles thrown at him after his team's first goal.
“The FA strongly condemns the unsavoury incidents this evening involving both the Manchester United team coach outside West Ham United's Boleyn Ground and objects thrown from a section of the home support during the game,” it said.
“We will work closely with both clubs and the Metropolitan Police to fully investigate these matters.”
A short video surfaced on Twitter which seemed to be filmed by midfielder Jesse Lingard and showed Manchester United's players lying on the floor of the bus.
Lingard could be seen pulling faces at the camera and shouting “Mummy, mummy!” as players shouted, laughed and swore.
Phil Jones, Michael Carrick and Adnan Januzaj, all wearing their club suits, were seen squeezed together on the floor in the aisle between the seats.
Manchester United captain Wayne Rooney later said the vehicle was “smashed up”.
“We know it's a big game for West Ham, a big night for them, leaving the stadium, but I'm sure West Ham as a club will be disappointed with what the fans have done,” Rooney told Sky Sports television.
“It wasn't nice,” he said.
The Times called it a “night of shameful violence” and Guardian columnist Barney Ronay criticised the lack of crowd control.
But West Ham co-chairman David Sullivan said the bus had not been damaged and blamed United for not arriving earlier.
“I don't understand why United couldn't get here at four o'clock,” he told BBC Radio 5 Live. “They could have got here early. They knew it would be busy. It's crazy.
“There was congestion in the street and they couldn't get the coach in. There were people around the coach, but there was no attack on the coach.
“If you check the coach there won't be any damage to it.”
United manager Louis van Gaal echoed his captain, Rooney, saying: “What do I have to tell? The images tell everything.
“The way we have been received is not the proper way,” he added.
Police said that one officer and a member of the public were injured, but there were no arrests.
“We are aware that a number of items were thrown towards Man Utd's coach this evening,” the Metropolitan Police football unit wrote on Twitter.
“Where criminal offences are committed we will seek to work with the clubs to bring those that break the law to court.”
West Ham are moving to the nearby Olympic Stadium at the end of season and a farewell ceremony followed Tuesday's game. – AFP
Original source: FA to probe attack on United bus