Purse is struggling with the hamstring strain that forced him out of the goalless draw with Derby at the weekend and could undergo a late fitness test.
Richard Hinds replaced Purse on Saturday and is likely to continue if Wednesday's captain fails to make it.
Varney, on loan from Derby, missed out against his parent club but returns to give manager Alan Irvine, who started with Marcus Tudgay and Leon Clarke last weekend, further options up front.
Winger Jermaine Johnson missed out against Derby and is still nursing a hamstring problem, so Etienne Esajas could return to the starting line-up.
Irvine's side, who have drawn their last three league games, will leapfrog relegation rivals Watford in the bottom six if they win.