New signing Gardner was sent off in Tuesday’s 2-1 defeat at Preston and serves a one-match ban while Davis completes his two-game suspension for accruing 10 yellow cards.
Skipper Michael Morrison is out with a groin problem with fellow defender Ryan Shotton also carrying a groin injury.
Striker Clayton Donaldson is not expected back until early next month as he continues to recover from an Achilles issue.
Ravel Morrison could be in contention for QPR. The forward has been building up fitness since his deadline-day arrival, but missed last week’s loss to Huddersfield.
Joel Lynch (hamstring) may also return for Rangers. Jack Robinson (hamstring) and Steven Caulker (hip) remain out.