German newspaper Der Spiegel claims they have fresh evidence that proves the Court of Arbitration's verdict was wrong, but City have strenuously denied the new claims, saying they are a 'cynical attempt to publicly re-litigate'.
City successfully overturned a two-year European football ban earlier this month, with the independent judicial body finding that they had not breached Uefa's financial fair play regulations.
Der Spiegel had claimed that seven leaked emails, revealed by Football Leaks, showed that the Premier League club had disguised owner investment as payments from sponsors in a bid to circumvent financial rules, leading to the punishment from Uefa.
However, CAS found in City's favour that the seven emails had been taken out of context, thereby reversing the sanction handed by the football body.
But now the German publication claim they have a new batch of emails that they say prove not only City's guilt in defying financial rules, but that they lied to CAS during the hearing.
The newspaper does not specify the details contained in the emails, but maintain that City have committed wrongdoing in regards to their financial arrangements.
The former Premier League champions have always firmly denied the allegations, saying that the claims are part of a 'clear and organised' assault on the club's reputation, before adding that the latest allegations are part of 'a cynical attempt to publicly re-litigate'.
'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.'