The Premier League is understood to be confident that any legal attempt to reverse its decision not to dock Sunderland points for fielding an ineligible player would fail.

The Observer exclusively revealed on Sunday that Norwich, Fulham and Cardiff have instructed lawyers to challenge the decision to merely fine the Wearside club a six figure sum despite their deployment of Ji Dong-won in four league games.

In theory a points forfeiture could dictate that Gus Poyet's side were relegated rather than, as seems most likely, Norwich, but the so called "gang of three" appear to have overlooked the formidable strength of Sunderland's potential defence.

With no Premier League appeal mechanism available any action would involve suing the governing body at vast expense. Logistically it would be virtually impossible for a case to be heard by a court before August and the start of next season.

Although there have been a string of precedents in which clubs lost points for selecting ineligible players, Premier League rules allow scope for leniency in situations such as Ji's which involve a lack of international clearance.

Moreover the South Korea forward was officially registered with the Premier League and Football Association as part of Sunderland's 25-man match-day squad at the time of the offence. Both governing bodies had ratified his inclusion on their electronic extranet systems.

While a clerical error on an online Fifa form meant that Ji technically lacked international clearance after a loan stint at Augsburg last season, Sunderland remain adamant the form was originally filled in correctly but information was subsequently deleted by accident during its electronic submission.

With Ji having returned to Augsburg in January the mistake would almost certainly have gone undetected had Sunderland not noticed that his name failed to feature on a Fifa list compiled for doping control purposes and immediately contacted the Premier League.

Due to the mitigating factors it issued a discreet fine, details of which later leaked to a national newspaper. At the time Sunderland said: "The club has never accepted any wrongdoing but did acknowledge that a technical fault occurred."

The hushing-up of the incident understandably prompted annoyance but the Premier League still acted within the remit of rule 6.9 of its handbook. It states: "Any club found to have played an ineligible player in a match shall have any points gained deducted from its record and have levied upon it a fine. The company may vary this decision in respect of the points gained only where the ineligibility was due to the failure to obtain an international transfer certificate."

Paolo Di Canio's side gained only one point – in a 1-1 draw at Southampton – during the four league games in which Ji was involved, primarily as a substitute making minimal impact. It was initially thought Sunderland's rivals accepted that docking them a point would have been overly harsh with a heavy fine representing an appropriate sanction.

The issue was aired during a Premier League shareholders' meeting in early April and no club objected. This fact could weaken any legal case.

The ruling body invited anyone harbouring concerns to ask for further information as to the reasoning. Given the horrendous cost of relegation, three clubs, believed to be relegated Fulham and Cardiff as well as Norwich, have done so, two in early April and one more recently. Sunderland and the Premier League await their next move with interest.

The Norwich manager Neil Adams refused to be drawn on his club's next move following their 0-0 draw with Chelsea which all but ends their Premier League survival hopes. "It's not for me. I'm not ducking that one, but it's for the board," he said. "They'll look at it, I'm sure, but I wouldn't want to comment on that. It's not a football matter. But I'm well aware of what's happened. They're aware of it, and I'm aware that they're aware of it. But that's for them. My brief is football matters. That's the legal side."