The alleged misdeed surrounded Radamel Falcao's loan from Monaco to Manchester United in 2014.
Another day, another big story, as the Football Leaks investigative project throws up something new.
The latest claim concerns AS Monaco and Man Utd, with the report stating that the two clubs organized "a friendly match" - which ended up never happening - to cover a €4m from United to the French club as part of the loan deal for striker Radamel Falcao.
French news outlet Mediapart have reported that the Manchester club wanted to pay €4m of the €10m loan fee, based on the Red Devils finishing in the top four. However, French league rules prohibit performance based clauses being inserted into contracts.
Based on findings from a Mediapart investigation - via Get French Football News' translation - they report: "The deal was such that Manchester United would pay €6m plus €4m in bonuses if the English club finished in the top 4 of the Premier League.
"Performance bonus clauses were illegal according to LFP regulations, and thus this clause was left on the second draft of the loan contract.
"The two clubs found a way of including the €4m in the deal, but excluding all mention of it from the legal paperwork.
"On 1st September 2014, Manchester United and Monaco signed two contracts together. One was a €6m loan deal for Falcao, and the other was an agreement over a friendly match that Manchester United would pay AS Monaco €4m for."
As the friendly was approaching and in-line with the investigation, it was cancelled, as Man Utd manager at the time Louis van Gaal confirmed that he "did not want to have another friendly game after this summer tournament" - yet the money was still transferred to the French club.
The 'secret contracts' - referred to by the investigation - suggests Monaco have a history of tainting transfers with these type of illegal practices. The report makes reference to the contract of Falcao from Atletico Madrid to Monaco transfer containing 'strange stipulations'.
The investigation goes on to report that the contracts for Monaco players Ricardo Carvalho, Eric Abidal and Jérémy Toulalan all signed 'secret' contracts when moving to the south of France.
If reports are revealed to be true, Manchester United and Monaco could face serious sanctions for deceiving French league authorities.