The Republic of Ireland international is said to be training with the club with a view to a year-long loan deal after a troublesome season with the Premiership outfit.
Reid spent most of the campaign on the sidelines through injury and suspension and is looking for a move away - albeit on a temporary basis - in order to regain some form and fitness.
The irony of Reid's return will not be lossed on many Millwall fans, who remember the player's comments about joining Rovers because he wanted European football...