Former Huddersfield Town man Smithies, 25, replaces Rob Green after he was sent off in Saturday's defeat by Nottingham Forest, while Jamie Mackie and Alejandro Faurlin make their return to the QPR bench.
QPR have won only one of their last 13 league meetings with Blackburn, drawing five and losing seven.
Queens Park Rangers: Smithies; Perch, Onuoha, Angella, Konchesky; Tozser, Henry, Phillips, Luongo; Austin, Chery
Subs: Lumley, Hall, Hill, Gladwin, Doughty, Faurlin, Mackie
Blackburn Rovers: Steele; Henley, Duffy, Hanley, Spurr; Marshall, Guthrie, Evans, Conway, Koita; Rhodes
Subs: Raya, Kilgallon, Delfouneso, Olsson, Lawrence, O'Sullivan, Akpan