The Scotland international, who suffered a ruptured Achilles last March, played 50 minutes for the Seagulls' under-21s against Crystal Palace on Monday.
Mackail-Smith is likely to need at least one more reserve run-out before being considered for the first team, and all being well he could return in the FA Cup against Hull on February 17.
He told the club website: "I feel the sharpness slowly returning, the legs are getting a bit more used to running about and the brain is getting closer to understanding what my feet want to do.
"It was my decision at half-time regarding how I felt and I wanted to come out and do a bit more. I didn't have any problems.
"There is another game next week so I will probably be involved with that, then there is the (first-team) game against Leeds and I would like to be involved with that as I always score against them, but I don't think I will make that.
"It is just a case of doing bits and pieces then it is probably down to the gaffer and the physios when I can come back, but there are four homes games in a row so it would be nice to be in one of them."