Ashton's career was cut short in December 2009 during what should have been his prime at 26 after the one-time England star was forced to concede defeat in his long-standing battle with an ankle injury.
The problem was picked up on international duty in August 2006 during a training ground incident with Shaun Wright-Phillips.
Hammer blow: Ashton was injured on international duty in August 2006, before England 4-0 win over Greece at Old Trafford
Although Ashton returned from a long absence and eventually made his England debut in 2008 against Trinidad & Tobago, he never fully recovered from the knock.
The former Norwich forward, West Ham's record signing when he arrived from Carrow Road in 2006, recently settled a private compensation claim with the FA over the matter.
Legal action: Sullivan may reluctantly force the issue through the courts
But West Ham are yet to receive anything since the player's retirement and Sullivan has now warned he is ready to pursue the matter in the courts.
'We will have to issue a writ shortly, but it's the last thing I want to do because I don't believe people in football should be suing each other,' Sullivan told The Guardian.
'For West Ham to get nothing is appalling. Years after the injury and several years after the retirement, they have never offered us a penny. That can't be right.'
Accusing the FA of not honouring their commitments, Sullivan added: 'You would think the FA would be honourable and say we accept that he retired as a result of the injury he got training with England.
'He battled on and played games subsequently but was never the same and, ultimately, the ankle broke down. It's poor of the FA not to honourtheir commitments.
'Their insurance company are trying to argue that because he played 30 games after the injury, even though he retired as a result of the injury, they're not liable.
End game: Ashton, who made his England debut in 2008, was forced to retire through injury a year later
'But it's not like he retired because of anything else other than theankle, which was smashed to bits because of [Shaun] Wright-Phillips.
'It was an accident and these things happen, but the FA should pick up the bill.'
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Explore more:People: Dean Ashton, Shaun Wright-Phillips, David Sullivan Places: Norwich, United Kingdom Organisations: Football Association