Tributes at Leicester City Foootbal Club following a helicopter used by club owner Vichai Srivaddhanaprabha, crashing into flames in a vehicle park near the stadium shortly after 8.30pm on Saturday evening.
A number of Man United players have taken to social media to pay their respects to the chairman, the two members of his staff - Nursara Suknamai and Kaveporn Punpare - and pilot Eric Swaffer and his partner Izabela Roza Lechowicz, who all died in the crash.
He said: "RIP Vichai Srivaddhanaprabha".
No one on the ground was believed to have been injured, they said. In April, Vichai bought Bangkok's tallest building for US$423 million (RM1.77 billion), renaming it King Power Mahanakorn.
O'Neill, who managed the Foxes from 1995 to 2000, told BBC Radio Ulster: "He went into the community, he made donations to the universities, donations to the hospitals, and the Leicester people took to him".
Vichai Srivaddhanaprabha's son and widow were seen laying a wreath among a sea of tributes from fans outside the stadium, including flowers, football scarves and Buddhist statues.
According to Forbes magazine, Vichai was the fifth-richest person in Thailand with an estimated net worth of $4.9 billion.
Leicester's next game, which had been scheduled for Tuesday against Southampton in the League Cup, has been postponed.
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Supporters pay tribute at Leicester City Footbal Club following a helicopter used by club owner Vichai Srivaddhanaprabha, crashing into flames in a auto park near the stadium shortly after 8.30pm on Saturday evening.
Leicester City fan and former player, Gary Lineker, battled through the "most difficult" Match Of The Day he has ever hosted on Saturday and has since paid tribute to the chairman on Instagram. Eyewitnesses say the chopper just cleared the roof of the stand as it developed a snag and crashed onto the auto park. Police have already handed the file over to air accident investigators, while some eyewitnesses hailed the pilot as a hero for steering the plunging helicopter away from the still-busy stadium. Moments earlier, the AgustaWestland AW169 had risen from the center circle and cleared the stadium roof before it spiraled out of control and plummeted into an adjacent carpark in flames. "As far as we are aware nobody around the vehicle park was caught up in this problem".
DMU's rowing club highlighted the inspiration that Mr Vichai had given them and thanked the emergency services for their response to the crash.
"Today, our inspectors in Farnborough will start working on the recorder, which was subject to intense heat as a result of the post-accident fire".
After pumping millions of pounds into the club, he helped steer them back into the top flight in 2014 before they stunned the sport by beating the likes of Manchester United, Liverpool and Chelsea to become champions of England.
Jamie Vardy, Kasper Schmeichel and Harry Maguire - as well as manager Claude Puel and the rest of the squad - did a lap of the cordon placed around the flowers.
But it was not purely the financial investment he made in the club that had a big impact - it was the fact that he invested himself in the club that made him special.
The wedding of Vichai's daughter Voramas Srivaddhanaprabha in 2017 was attended by current King Maha Vajiralongkorn's daughter as well as generals of the junta that seized power in 2014.
The duty-free business got a big boost in 2006 when it was granted an airport monopoly under the government of then prime minister Thaksin Shinawatra, and it continued to prosper even after Thaksin's ouster in a coup that year.