The Scotland striker has been sidelined for more than a year after rupturing his Achilles against Bristol City last March.
But Mackail-Smith fired himself into contention for the trip to Oakwell with two goals for Albion's Under-21 side in a 2-2 draw with Charlton.
Assistant-boss Nathan Jones told the club website: "It was fantastic to see him back.
"He showed a real desire, looked as close to the CMS we know. His first goal was typical of him - he took it really well. For his second he showed real potency and strength.
"He has shown in that game he is capable of playing 90 minutes, scoring in injury time and that he's ready now.
"I am sure he will be full of adrenaline and desire and we are hopeful he will be an important player for us towards the end of the season."