The Premier League has agreed to provide Fifa with any "assurances and explanations" it needs into how West Ham's breach of rules was handled.
The West Ham saga has prompted concern from Fifa
The Hammers were fined £5.5m for irregularities over the signing of Carlos Tevez and Javier Mascherano but they escaped a points deduction.
Fifa president Sepp Blatter said he is "monitoring the situation carefully".
But Fifa has told BBC Five Live that it is not re-examining the evidence with the aim of testing the ruling.
West Ham broke two Premier League rules by entering into a private agreement with a third-party company when they signed Argentine pair Tevez and Mascherano in August last year.
The simple answer is why not have 21 clubs in the Premiership next season
Sheff Utd chairman Kevin McCabe
Mascherano has since moved to Liverpool, while Tevez stayed in London and played an influential role in West Ham's successful battle against relegation - scoring seven goals in the club's last 10 games.
Sheffield United, who went down on the final day of the season, are leading the fight against an independent commission's decision not to punish the Hammers with a points deduction.
The Blades, who are being supported by the likes of Wigan, Fulham, Charlton and Middlesbrough, are also concerned that West Ham may still have been breaking Premier League rules after the ruling on 27 April.
"It is up to the FA Premier League to find a way round this exceptional circumstance where a club which has played by the rules has been relegated at the expense of one club who have fielded ineligible players," said Sheffield United chairman Kevin McCabe.
"The simple answer is why not have 21 clubs in the Premiership next season and relegate four of them at the end. It is not my decision to make but it seems like a very simple solution."
The Premier League has argued that it has no case to answer in regards to West Ham's punishment because all 20 Premiership clubs agreed to the disciplinary system in place.
However, that has not stopped Sheffield United pursuing their case and Blatter's intervention may encourage them.
A Premier League statement later read: "We have implemented our rulebook and processes to the letter in this matter and we are more than happy to give Fifa any assurances or explanations they need."
Meanwhile, MP's are calling on the Premier League to "clarify the rules" over third party ownership.
Nine MP's have signed a House of Commons motion condemning the decision as "lenient" saying it shows that "advantage can be gained by cheating".