The media outlet claim that the Championship side are reluctant to grant the midfielder a move amid speculation of a potential switch to Scottish side Rangers.
“Toumani Diagouraga has handed in a transfer request at Brentford which has been rejected by the Championship club,” the report by Sky Sports states.
The 28-year-old midfielder has been heavily linked with a move to Rangers with former Brentford boss Mark Warburton currently in charge of the Ibrox club.
Diagouraga has fuelled speculation in recent days by telling the Scottish Sun of his interest at moving north of the border, highlighting his desire to work with Warburton again.
“I'm aware of Rangers' interest and I'm very flattered by it. I know they are a massive club and, of course, I'd be very interested in playing again for Mark," he explained.
The holding midfielder has been a key cog for Brentford since joining the Bees from Peterborough in 2010, playing over 200 league appearances for the club.
He has been an ever-present figure in Brentford’s side this season, helping the West London club overcome a somewhat disappointing start and climb the table towards the playoff positions.
New Brentford boss Dean Smith will not want to see him go, yet with the player intent on leaving he may have no other choice than to sell him for a price deemed acceptable by both clubs.