Bayern Munich chief executive Karl-Heinz Rummenigge has criticised City for their refusal to discuss Jerome Boateng's sale and feels they may be denied the chance to play in the Champions League.
Boateng, who joined City for £10 million from Hamburg last summer, struggled with injuries during his debut season in the Premier League and has made clear that he would like to force through a move to Bayern.
However, although the player has already agreed the terms of a contract with Bayern, it appears a deal remains nowhere near complete.
"They are using a tactic I've never seen," Rummenigge said. "They don't respond, even if we try to contact them."
City have already signed two defenders in the transfer window, Stefan Savic and Gael Clichy, and Rummenigge added: "I think they are going to have 48 players under contract but according to Financial Fair Play they can have only 25.
"According to their last balance sheet, if I'm correct, they're down £127 million. Maybe they still have a trick up their sleeves but I'm not sure that they will be permitted to play in the Champions League."
City chief executive Garry Cook has revealed the club has held a number of meetings with UEFA about Financial Fair Play.