The remarkable defeat of Croatia in Zagreb and spirited display in the 3-2 loss to England at Wembley felt like green shoots of recovery after the dire results which sank the 2014 World Cup qualifying campaign. But the visit of the Group A leaders on Friday will amount to the toughest examination so far according to McGhee.
Belgium are currently tenth in the Fifa world rankings, four ahead of England, and are three points clear of Croatia in the group thanks to the latter's defeat to Robert Snodgrass's goal in June.
The squad for Hampden includes Christian Benteke of Aston Villa, the Chelsea trio of Kevin de Bruyne, Eden Hazard and Romelu Lukaku, Zenit St Petersburg's Axel Witsel and Tottenham's Moussa Dembele. Vincent Kompany, the Manchester City centre-half who scored in their 2-0 defeat of Scotland in Brussels last October, is out injured.
"I think they are stronger than Croatia and England just now," said McGhee. "They have found their way. England haven't quite gelled or found the formula to get the best of the group they have. I also think we caught Croatia a bit short. We cannot deny how much they missed Luka Modric and how we benefited from that. Belgium are a team on song.
"We have to prove that Zagreb was a turning point for us. One of the things that has changed after the last two games is that anyone who comes to Hampden on Friday is expecting to see a certain type of performance and a certain style of play. Results will be good and bad but the players and the public, the supporters, have got to know that when they come to Scotland this is what they are going to see.
"We know the strength of the Belgians and we know that two games, one of which we actually lost, don't turn everything around. But there were a lot of positives from those performances that we can hope to continue into the Belgium game."
Rangers left-back Lee Wallace, Craig Bryson of Derby County, Chris Burke of Birmingham City and, surprisingly, the Hibs midfielder Kevin Thomson were called into the squad yesterday as Hull City pair George Boyd and Allan McGregor withdrew after West Bromwich Albion pair James Morrison and Graham Dorrans.
Manager Gordon Strachan called in the four to insure the squad against the possibility of further injuries or suspension. Seven players are one booking away from being suspended for the second half of the double-header in Macedonia next Tuesday.
Strachan and McGhee had different views on whether a gamble could have been taken on Sunderland's Steven Fletcher. He made his first competitive appearance in five months and scored against Crystal Palace on Saturday evening.
Strachan thought it too early to rush him back after an ankle injury while McGhee said: "We know how good a player he is and with the retirement of Kenny Miller he is even more important now. The manager was not tempted to bring him back. I was, but Gordon ruled it out right away. We want him back as quick as we can, but we want the lad back fit."
Barry Bannan, meanwhile, was due to join the squad last night after being given permission to remain in England to finalise his move from Aston Villa to Crystal Palace.