UEFA opened a "formal investigation" into Paris Saint-Germain on Friday after the French club broke the world transfer record to sign Neymar.
European football's governing body said it would look at whether PSG had violated its Financial Fair Play (FFP) rules.
"The investigation will focus on the compliance of the club with the break-even requirement, particularly in light of its recent transfer activity," UEFA said in a statement.
PSG signed Brazilian striker Neymar for a world-record 222 million euros ($264 million) on August 3 and completed a loan move for Kylian Mbappe on Thursday in a deal that includes an option to buy the French teenager for 180 million euros.
"In the coming months, the Investigatory Chamber of the UEFA Club Financial Control Body will regularly meet in order to carefully evaluate all documentation pertaining to this case," the statement added.
"UEFA considers Financial Fair Play to be a crucial governance mechanism which aims to ensure the financial sustainability of European club football."
The FFP system was first approved by UEFA in 2010 to try and combat soaring debts in the game.
From 2013 to 2015 clubs could only post a net total loss of 45 million euros, which was reduced to 30 million for the next three years, running until 2018.
Non-compliance with the rules can result in a series of disciplinary measures, ranging from a warning to the deduction of points, and even exclusion from European competition.
PSG have already incurred sanctions for a previous violation and were slapped with a 60-million-euro fine, 40 million of which suspended, in 2014, and saw their squad for the Champions League cut from 25 to 21 players.
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