Douglas is out of favour at Elland Road and remaining at Leeds would mean the Scottish defender is unlikely to play regular football.
Blackburn and Watford have shown interest in Douglas, but despite the Hornets being keen, he is Ewood Park bound.
Douglas is currently having a medical at Blackburn in advance of completing a move to the Championship side before the domestic window closes on Friday evening.
He is expected to link up with Tony Mowbray’s men on a season-long loan deal and will be looking to clock regular game time in the Championship.
Douglas helped Wolves win promotion from the Championship and then repeated the trick with Leeds.
However, on both occasions he quickly found Premier League football to be out of reach, moving on from Wolves and now being set to move on from Leeds.
Douglas’ arrival will strengthen Mowbray’s defensive options and the Leeds man will link up with a side sitting sixth in the Championship standings after taking seven points from their opening four league games.