'A 2012 Olympic legacy? It could be Leyton Orient going out of business'

They were cleaning the seats in the away section of the old East Stand at Brisbane Road yesterday, a small band working their way along row after row, a spray and a polish for seat after seat; Leyton Orient are readying themselves for the footballing equivalent of a royal visit. On Sunday afternoon, Arsenal will be in this modest corner of east London, sprinkling a little Premier League stardust, or rather helping to add thousands of badly needed pounds to the club coffers.

"It has made us just short of £800,000," says Barry Hearn, the club's chairman, of their trip to the fifth round of the FA Cup. "We're a club that on average loses between £600,000 and £1m per year – it shows what the Cup can do." What it certainly does is brighten the club's immediate future, on and off the pitch.

On it, one defeat in 20 games and away victories at Norwich and Swansea send the League One side into Sunday's tie on a high. There is talk of Hearn funding trips to Las Vegas if Arsenal are, somehow, beaten or the play-offs reached come the end of the season. But climb to the third floor of the West Stand and look west, towards the high rises of the City of London and the reason for growing fears for the long-term future of the club is obvious. The dark cloud is not on the horizon, it is much, much closer.

Last week's decision to name West Ham United as the preferred bidder to take on the Olympic Stadium post-2012 Games was a hammer blow to Orient, and, according to Hearn, potentially a fatal one. The Olympic Park is little more than a hefty punt away, the A-shaped floodlights of the stadium visible above the frosted icing covering of the basketball arena and the velodrome's polished curves.

Tomorrow, Hearn will meet with Richard Scudamore, the Premier League's chief executive, to discuss regulation 1, part 6.5 of the top flight's rule book, which says that clubs cannot move to another ground if it "adversely affects clubs having their registered grounds in the immediate vicinity of the proposed location".

Hearn has already written to the Primer Minister, two ministers involved in the stadium decision, Jeremy Hunt and Hugh Robertson, as well as Boris Johnson, the mayor of London, requesting they hold off "rubber stamping" the Olympic Park Legacy Company's decision until Orient's case is properly heard. He is waiting for a reply. "I am very concerned the government is hiding behind the Premier League," he says. It's Barry Hearn against the world, and that, it seems, is just how he likes it.

"I don't anticipate a lot of support," he says of the battle that lies ahead, before adding: "I don't like bullies and I don't like being bullied." His chances of stopping West Ham taking up residency on their doorstep, where Orient have been based since 1937 – and they have been playing in the area since 1881 – are slim indeed, but it will not stop him trying. "I want respect," he says. "I want the effect on Leyton Orient, not just as a business but in the community, to be considered. This is not a game of poker, this is a game of life and death. We are talking about the future of a 130-year-old club. Choosing my words extremely carefully, this is a very, very difficult time for Leyton Orient."

Sunday provides an escape, and one that a showman like Hearn, with his boxing roots and local pride, is not going to pass up. The Cup itself is here and he takes it from his manager, Russell Slade, holds it with a smile spreading over his face and plants a kiss on it at the request of a photographer. One of the Cup's bodyguards – it comes with two – looks worried.

"I get demoralised by the way football's going, it's a flawed business, but I've had so much fun this year," he says. "They talk about the Champions League, but the FA Cup has history. History is important for all of us, it sets out where we are, gives us memories to pass down to our children and grandchildren."

Brisbane Road will be full to its 9,300 capacity on Sunday, around double their usual attendance. When, and it is almost certainly when, West Ham move in, Orient's concern is those modest figures go west, literally. Karren Brady has already spoken of West Ham offering cheap tickets and special family deals to try and fill their new 60,000-seat home, and Hearn is all too aware of the lure of the Premier League, if (and this time it is an if) West Ham are still a top-flight club. Leyton Orient of League One, or even the Championship, would not be able to compete.

"Once Sunday is finished we are back to normal and I'm dealing with a problem here," says Hearn, who took over at Orient in 1995. "I have a responsibility here and this could put this club out of business. This could be the end of Leyton Orient." He is asked what he wants, and he says he doesn't know yet, nor is he entirely convincing on why Orient have waited so long to make their case so vocally.

Outside on the community pitches, groups of schoolchildren are playing six-a-side games; Orient pride themselves on their community involvement and their place in the area. It does not take long to walk past the two pitches, past the large car dealership at the end of the road, turn right past the Greek Orthodox church, cross a railway bridge and reach the edge of the Olympic Park, a large chain-link fence and mounds of earthworks steadily being landscaped for the greatest show on earth.

"We're all from the East End, this is our patch and we are honoured to have the Olympics here," says Hearn. "It is the greatest thing to happen to the East End in my lifetime, but it is ironic that the legacy of the Olympics could be the demise of the local community club. That would be against the ethos of the Olympics, the ethos of sport for all that revolves around community clubs like this."