West Ham's request to move to London's Olympic Stadium after the 2012 Olympic Games has been formally rejected.
Artists impression of the 2012 Olympic Stadium
The London 2012 Olympic Board has confirmed the stadium's 80,000 capacity for the Games will be be reduced to just 25,000 afterwards.
Athletics will occupy the stadium, whose reduced capacity is 10,000 less than the Hammers current home.
Leyton Orient chairman Barry Hearn confirmed he is in talks about moving the League One club to the stadium.
London organising chairman Lord Coe had told BBC News24: "At Games time the stadium will hold 80,000. But afterwards it will have 25,000 seats.
"We have always made it clear we will go forward with track and field facilities but we will encourage other sports to become involved."
As a condition of its winning bid, the London Board must provide a stadium with an athletics and community sports-for-all legacy, which involves keeping the track.
A statement from the board said: "The board reiterated the priority was to deliver an Olympic stadium on time and on budget.
"The board unanimously decided that it would not be possible to deliver this in collaboration with West Ham or any other Premier League football club, due to the number of design changes and associated time delays the West Ham proposal would incur.
"The board discussed a report on legacy that shows the Living Stadium concept - with a mixed sport offering combined with commercial, school and community use - is the most compelling."
Orient chairman Hearn is keen to move the club away from their current Brisbane Road home.
He insisted: "We are the frontrunners for potential usage of the stadium, but there is a long way to go.
"In principle, Leyton Orient fits the criteria as occupants of the stadium."
The Hammers' new owner Eggert Magnusson has previously described the prospect of leaving Upton Park for the showpiece venue as a "dream".
Magnusson had no objection to the stadium retaining track and field facilities - probably with removable seats.
The Mayor of London, Ken Livingstone, has told the Olympic board he is anxious to assist and support West Ham's plans for developing and securing their future.
After discussions with Mr Livingstone, West Ham are exploring with the London Development Agency (LDA) the possibility of relocating and building a new stadium.
One of the options being considered is a site next to West Ham underground station.