Gordon Strachan begs to differ. There has always been a perception among those who do not follow either side that playing for Celtic or Rangers offers players an instant fast-track route to international football. McGregor's inclusion in the 26-man squad to face Germany next month on the back of just seven Celtic appearances would seem to give further weight to that argument.
The man who picked him, though, sees it differently. Strachan points towards McGregor's decision to go out loan at Notts County in League One last season as evidence of a player who has made a conscious effort to ignite his career and is now reaping the benefits. The Scotland manager is big on those who have elected to extricate themselves from their comfort zone to test themselves in what he describes as "the real world". If they have subsequently endured periods of adversity and come through the other side then all the better.
In extolling McGregor's achievements, Strachan namechecked other Scottish sportsmen and women who he felt had been knocked down but got back up again. There was praise for boxer Charlie Flynn, the punching postie who took gold at the Commonwealth Games, and Eilidh Child, a silver medallist in Glasgow in the 400m hurdles who took gold a few weeks later at the European Championships. Both, Strachan felt, had suffered hardship at points in their careers but rebounded to taste subsequent glory.
It was a similar story for McGregor, who was part of a County side that spent the majority of the campaign fighting against relegation, eventually surviving by the skin of their teeth. The bold decision to put himself into that scenario has earned him not only the respect of the Scotland manager but also the chance of a debut cap against the world champions.
"We closet kids nowadays and take them along to play under-21 games in a training ground with no pressure," he said. "They go back on to the bus and the coach isn't allowed to raise his voice to them. Whether they get beat or not, nobody says 'boo' to them.
"At Notts County Callum was playing with guys who actually had to win to get a bonus to make a difference to their lives. He had to stand in front of 5000-6000 people who are booing and screaming if he hits a bad pass - can he come back from that?
"It's a reality and he has dealt with reality. He could have sat there, walking about Glasgow saying, 'I'm a Celtic player', but he chose to be a Notts County because he wanted to learn the game. I like that. Character is needed in football.
"You can have all the skill but character is a huge thing. In life you are going to be really tested somewhere and if you don't get tested when you're younger, you'll never be able to handle these things."
Strachan recalled his own insecurities following a difficult introduction to life as a player.
"I'd go home crying from games when I was a young boy because I thought I'd blown my chance of being a football player," he added. "I got beat 6-1 but coming back from that, dealing with that, is reality. That's life. It's like the wee boxer guy, Charlie Flynn, who won the gold medal. He's real - he's had to get knocked down and back up.
"He's a postman, he's been beaten a couple of times but he's come back and when it comes to the crunch, his character has shown.
"Look at Eilidh Child, I'm sure she's been beaten. She hasn't been told, 'ach it doesn't matter, you did great.' That's what we need to watch now - that we just don't make kids who are lovely technically, but if you say boo to them, they will run away.
"Sometimes when you put them in the real world, it's like putting a domesticated animal in the jungle. They have to have character.
"Every player I played with had it, to handle the abuse from a manager, the crowd, and the media.
"We need to watch we don't get away from reality."
There were more rags-to-riches tales in this Scotland squad than in a series of Hollywood movies. Craig Gordon is back in the fold having revived his career at Celtic after two years on the sidelines. Andy Robertson has recovered from being rejected as a youth player at Celtic to go from the Scottish third division to the Barclays Premier League in the space of 15 months, while Alan Hutton is back playing again with Aston Villa having been frozen out for two seasons.
"Their character is tested in later life but because they had all sorts of knockbacks in younger life then they can deal with it," enthused Strachan. "On the field your character is tested in big games. You never know when the game comes that will test you."
Gordon's recall, at the expense of Matt Gilks, gives Strachan the choice of three excellent goalkeepers and against Germany there must be a temptation to play them all. Strachan admitted he was lucky to have such strength in depth.
"It's the toughest decision going. Neither of these guys have let me down - they've been terrific. And even Matt when he went in goals in Poland was great. So we are strong in that area. I just want to get to know Craig as the staff has changed since the last time he was in a squad, although he knows Jim Stewart.
"But it's about getting him back involved, getting to know him and having a look. I have to make a decision over Allan and David."