Manager Russell Slade has said Cardiff are looking at whether Juan Cala broke club discipline rules on social media.
Aston Villa boss Paul Lambert has defended his decision to send striker Darren Bent out on loan to Brighton.
The 32-year-old centre-back, who can number Chelsea, Stuttgart and Sporting Lisbon among his former clubs, has signed a one-year contract at De Kuip after leaving Brondby.
A statement published on Feyenoord's official website revealed Boulahrouz's deal in Rotterdam includes the option of a further year.
He left RKC Waalwijk for Hamburg in 2004 and made 35 appearances for Holland across eight years.