The former Cambuslang and Hawks stand-off suffered a knee injury after colliding with a goalpost during a training game of kick-tennis in September.
The injury kept Duncan out of Glasgow's six-game winning run which saw them rise to third in the PRO12 table with both Ruaridh Jackson and Scott Wight battling for the number 10 jersey.
Duncan told the Scotsman: "I'm just itching to get out there and put in a good performance because I know if I don't there are two guys clapping on the door.
"I was quite happy with the way I was going in the first three games of the season.
"I've added a more attacking mind-set to my game this year with Gregor Townsend coming in, and I was getting comfortable moving on the ball and feeding players off me.
"It's been nine weeks on the sidelines and it was a bit frustrating at how it all came about.
"It was a bit of kick-tennis on a Monday morning as a wee warm-up drill, and it was a game of nines verses tens and I wasn't going to let the nines win.
"One thing led to another and I ended up on the wrong side."