Diagouraga was one of Brentford's star players last season as he played an instrumental role in helping the club reach the Championship play-off semi-finals.
The all-action midfielder was voted player of the year by Brentford fans after a number of outstanding performances for the club in 2014/15.
Diagouraga's performances have not gone unnoticed among rival clubs, with Fulham keen to raid their London neighbours for the defensive midfielder.
Leeds boss Uwe Rosler is a big admirer of Diagouraga having worked with the player during his time in charge of Brentford and is thought to be keen on luring the French-born star to Elland Road.
Huddersfield are in the market for a defensive midfielder and Diagouraga is thought to be the top target on their wanted list, while Diagouraga's former Brentford boss Mark Warburton is keen on being reunited with the player at Rangers as he plots a return to the Scottish Premiership.
Brentford are, however, reluctant to lose one of their prized assets and are determined to fend off any interest in Diagouraga as they look to build on their success from last season.