Monaco owner Dmitri Rybolovlev has confirmed he is under investigation by police in the principality.

French media reported the billionaire's luxury Monaco apartment had been searched and he had been placed in custody on Tuesday before being freed later the same day.

In a press release published on behalf of Rybolovlev on Wednesday, it was confirmed the Russian businessman, ranked 242nd among the world's richest people, is "subject to judicial control" after being released, but "still enjoys complete freedom of movement" with no restrictions other than "communicating with persons concerned by the proceedings."

"We do insist on the fact that at this stage, Mr. Rybolovlev is presumed innocent and that this presumption and the rights attached to it should be strictly respected," a statement from the Monaco owner's lawyers said.

No details of the investigation have been confirmed, nor any potential breaches of the principality's law Rybolovlev may or may not have committed.

The 51-year-old, who made his fortune in the potash industry, bought Monaco for €1 in December 2011 with the club struggling in the French second division.

He invested heavily and saw the club win the 2016-17 Ligue 1 title and reach the Champions League semifinals the same season.

They have also twice finished runners-up during his ownership, but this season find themselves in the relegation zone after a disastrous start that saw title-winning coach Leonardo Jardim replaced by Thierry Henry.