Mackail-Smith has been absent for more than a year with a serious Achilles injury, but after scoring twice for the club's Under-21 side, assistant boss Nathan Jones believes that the Scotland international is ready to make an impact during the final weeks of the campaign.
The 40-year-old told the club's official website: "It was fantastic to see him back. He showed a real desire, looked as close to the CMS we know.
"He has shown in that game that he is capable of playing 90 minutes, scoring in injury time and that he's ready now.
"I am sure that he will be full of adrenaline and desire and we are hopeful that he will be an important player for us towards the end of the season."
Mackail-Smith has scored 21 goals in 81 games for Brighton.