His team-mates knew that, while he was not the biggest or strongest player in a side which included Bobo Balde, Johan Mjallby, Chris Sutton and John Hartson, they could depend on him in every situation.
Now, those qualities of total commitment and game intelligence have transferred with McNamara into management, where, again, it is as a team player that his core strength - and success - derives.
At Ibrox today, he will get the opportunity to take a signficant step up the managerial ladder he first alighted when he took charge of Partick Thistle as an interim rookie in 2011.
Victory over Rangers - even though Ally McCoist's side are operating two divisions below his Dundee United - will be a major feather in his cap, not least because it will confirm that McNamara and his young side do not freeze when encountering the big occasion.
For all the furore about choice of venue and ticket allocation, it is what the players on the park do which, ultimately, will determine the outcome.
And, with McNamara's cool guidance, despite the relative inexperience of rising statrs such as Ryan Gauld, John Souttar, Andrew Robertson and Stuart Armstrong, United are the bookies' favourites to book their place in the William Hill Scottish Cup final at Parkhead on May 17.
That would be a return to his old stomping ground for McNamara, and it would be fitting if it was there he could secure his first trophy as a manager.
During a decade playing at Celtic Park - which can be measured as five years of almost constant heartache and the next five of equally- frequent glory - he was often overlooked when the praise rained down on Henrik Larsson, Sutton, Hartson, Mjallby, Stilyan Petrov, Paul Lambert and Neil Lennon.
But, like the rest, the last name appreciated what McNamara brought to the side.
And, though he did not pick him out as a man most likely to make the switch from playing to management, Lennon recognised during his four years sharing a dressing room with him that the quiet man in the corner was soaking up the knowledge required to become a boss, and storing it away for days like today.
Lennon reflected: "Jackie is intelligent, and you could see that in the way he played.
"For Celtic, he performed in a variety of positions, including full-back and midfield, and was very consistent for the team and gained a lot of experience during his time here.
"Now he is making his mark as a manager.
"And, to be fair, he has a good backroom staff with him at Dundee United as well.
"Simon Donnelly, Darren Jackson and Jackie have been very close for a number of years now."
Lennon would not claim to be anything like as tight with McNamara as those other former Celtic team-mates.
And, when you see them standing in opposing technical areas - as they did last weekend at Tannadice when Celtic won 2-0 in the SPFL Premiership - there is a respect, but no indication of a strong friendship.
Indeed, not content with taking the points last weekend, Lennon set about scoring some more post-match when he revealed how he felt his side does not get the credit it deserves, and that is often overlooked how laden it is with talented young players.
That appeared to be a not-too-veiled swipe at how much attention is paid to United's crop of kids.
But, what Lennon is happy to echo is the praise given to the attractive, entertaining style of play McNamara has instilled since he moved to Tannadice from Firhill just over a year ago.
The Hoops boss concedes he did not suspect that the man whose playing career mainly centred on stopping the opposition would morph into a manager who insisted his team played this way.
Asked if he is surprised at how well McNamara has taken to the job, and, in particualr, to developing players, Lennon replied: "I am surprised a bit, but I am very pleased for him.
"Even when he was at Partick Thistle, his team played an expansive and easy-on-the-eye type of football.
"Jackie has taken that on to Dundee United.
"They had a bit of a lull midway through the season, but they look as though they are right back in form again.
"Now they have a very big game coming up in the semi- final, and that might have been praying on his mind going into the game against us last weekend."