Thomson, 24, featured for the final 13 minutes of Saturday's opening Clydesdale Bank Premier League game of the season against Falkirk.
"It'll take Kevin a period of time to get back to full match fitness and even then, it'll take a few games to get going," Gers boss Walter Smith told his club's official website.
"He is fortunate in the sense he has had the same injury before so he knows exactly what to expect in his bid to get back to fitness.
"Kevin plays in a deeper position in midfield so he can handle things a little bit better because you don't need the same sharpness that forwards require at their peak.
"He has been doing well enough in the games he has featured in so far, both during pre-season and on Saturday.
"We now have to move on to a situation where Kevin starts matches then comes off after a while rather than begins on the bench and comes on as a substitute.
"He is just about ready for that situation now and we are happy with the progress he is making."