City were originally banned from all European competition back in February after UEFA found them to be in breach of Financial Fair Play regulations. UEFA's Club Financial Control Body discovered that the club falsely inflated their sponsorship revenues and then had been deliberately obstructive when investigations began.
This investigation was instigated when a string of leaked emails were published in Der Spiegel via Football Leaks author and whistleblower Rui Pinto. However, UEFA's verdict was overturned in early July after City appealed the case at CAS.
Der Spiegel has now tabled fresh allegations. The paper claims (via Daily Mail) that it possesses a further batch of emails which not only prove the Citizens' guilt but also shows the club lied during the recent court proceedings.
Unsurprisingly, this has been vehemently denied by City who have consistently denied any wrongdoing.
"The questions and matters raised by Der Spiegel appear to be a cynical attempt to publicly re-litigate and undermine a case that has been fully adjudicated, after detailed proceedings and due process, by the Court of Arbitration for Sport," the club said in a statement issued on Thursday.
"Manchester City's policy remains not to comment on out of context materials purported to have been criminally obtained from City Football Group and Manchester City personnel."
How the situation will develop after this latest spat is unclear. CAS recently confirmed that no less than nine Premier League clubs wrote to them after the initial ruling, requesting that they did overturn the ban.
Arsenal, Burnley, Chelsea, Leicester, Liverpool, Manchester United, Newcastle, Spurs and Wolves all wrote letters pleading that City be excluded from European competition.