Chelsea and Aston Villa have reportedly been warned by UEFA that player swap deals will be monitored closely to make sure fees have not been inflated.
UEFA are believed to have taken issue with at least one previous deal, according to The Times.
In recent years Premier League clubs have paid sizeable fees to each other in instances where players have moved in each direction.
And there have been protests from rivals that this has been done with the aim of artificially increasing transfer income in order to comply with Profitability and Sustainability Rules.