Steffon Armitage is being held in custody at a French police station, his club Toulon have confirmed.
The 29-year-old flanker was taken in for questioning along with team-mate Xavier Chiocci, and should learn later on Thursday whether he is to face charges.
Twenty-four-year-old prop Chiocci was released without charge on Wednesday evening.
A statement on www.rctoulon.com read: "Rugby Club Toulon learned yesterday that two of its players, namely Steffon Armitage and Xavier Chiocci, had been taken into custody.
"Custody of Xavier Chiocci ended on Wednesday night, with no charges brought against him.
"Custody of Steffon Armitage was extended during the night, and a decision should be taken on Thursday.
"Rugby Club Toulon is awaiting the results of the investigation, and will, if appropriate, take the necessary sanctions to preserve the values that are dear to the club."
Armitage, the 2014 European Player of the Year, has won five England caps but was not under consideration for the RBS 6 Nations due to the Rugby Football Union's policy of not selecting overseas-based players.