The Saints midfielder suffered a bout of concussion following a clash during a recent League Cup tie against Rangers at Ibrox.
Davidson was carried off during that match and missed the win over Motherwell and draw with Dundee which followed.
Saints do have concerns over David Wotherspoon and Gary McDonald, who are both struggling with hamstring problems.
Ross County have no new injuries for their Scottish Premiership encounter against St Johnstone at McDiarmid Park.
Rocco Quinn is stifor the visitors as the midfielder recovers with a long-term hip injury.
County boss Jim McIntyre continued to reshape his squad last week by releasing Uros Celcer, Tim Dreesen and Jordi Balk.