Kenneth is training with his old club following his departure from the English League 2 side Bristol Rovers prior to Christmas.
The 26-year-old, a member of United's Scottish Cup-winning side in 2010, has spoken of his desire to play for his boyhood idols again having left Tannadice in the summer of 2012.
His spell in England was blighted by a series of injuries but McNamara has intimated that the former Scotland defender could return to the club if he can demonstrate that he is in the right condition to do so.
McNamara said: "Garry has been training with us but the biggest thing for him at the moment is fitness. He has not had a lot of games recently and he is not fit enough to play which doesn't help either of us.
"Garry is training away and we will have a look at him in the next week or two to see if it is going the right way.If he shows and improves then we will have a look at it. I have spoken to him about it but at the moment he is not fit enough to play.
"He has taken part in a couple of bounce games where it wasn't really fair to judge him. He wasn't tested properly but fitness wise I think he is a few weeks away. If Garry was fit, then it would be good to get him in right now but that is not the case."
McNamara's observations come at a time when he could do with reinforcements in defence. Gavin Gunning is due to undergo a scan on his hamstring after he missed the 3-0 defeat at Ross County having sustained the injury the previous weekend at Inverness. McNamara wants to ascertain whether Gunning will be out for any longer.
He said: "We are sending Gavin Gunning for a scan on his hamstring to find out whether he tore it against Inverness. I don't know whether he will be fit to face St Johnstone on Monday. If the scan comes back okay, then he might have a chance. "Regardless of the outcome, we will still be looking to add during the window. We are seeing who is available but as everyone will tell you, it is a difficult window in terms of getting players in that you want."