Borussia Dortmund chief executive Hans-Joachim Watzke has called for clubs who exploit “back-door funding” to be expelled from European competition.
Watzke's comments come immediately before his club's Champions League clash against Manchester City, who have been transformed into a major force by the wealth of benefactor Sheikh Mansour in recent years.
City's financial strength attracted thinly-veiled attacks from senior officials at two of their Champions League opponents, Bayern Munich and Napoli, last season.
Now Watzke wants sponsorship deals investigated to ensure all clubs conform to the incoming financial fair play guidelines of European governing body UEFA.
That could be perceived as a shot at City, who have shirt and stadium-naming deals with Etihad, state airline of the sheikh's emirate Abu Dhabi.
Watzke told reporters: "UEFA must find the thin line between sponsorship and excessive back-door funding - they must show strength to expel big clubs.
"No tycoon should be allowed to pump crazy money into a club with sponsorship from five companies he controls. If that happens, financial fair play will fail."