That's because the former Cardiff and Watford manager already felt CalMac could walk into any team, in any top European league.
What Mackay reckons showings in McGregor's 50th and 51st Scotland caps against Cyprus and Spain will have done is act as a jolt to Spanish as well as other leading international observers with no great regard for Scottish football.
Mackay, who handed McGregor his first cap against the Dutch during his caretaker stint in 2017, believes he would thrive among the elite.
That he chooses to dedicate his career to captaining Celtic only adds to Mackay's admiration.
The Ross County boss, preparing for Celtic's visit on Sunday, said: "Cal was just phenomenal against Spain.
"That was quite a game and result of the decade maybe! "The bit that really hammered it home was when Callum takes the ball 40 or 50 yards upfield with two minutes to go, teases and tricks, and almost nicks Scotland in for another goal.
"That's the point I believe Spaniards and other big clubs - would have been eyebrows raised, asking, 'Who the hell is that?' and, 'Can we sign him?'.
Diese Geschichte stammt aus der March 31, 2023-Ausgabe von Daily Record.
Starten Sie Ihre 7-tägige kostenlose Testversion von Magzter GOLD, um auf Tausende kuratierte Premium-Storys sowie über 8.000 Zeitschriften und Zeitungen zuzugreifen.
Bereits Abonnent ? Anmelden
Diese Geschichte stammt aus der March 31, 2023-Ausgabe von Daily Record.
Starten Sie Ihre 7-tägige kostenlose Testversion von Magzter GOLD, um auf Tausende kuratierte Premium-Storys sowie über 8.000 Zeitschriften und Zeitungen zuzugreifen.
Bereits Abonnent? Anmelden
ATA BHOY BRENDAN
Rodgers vindicated as he proves he can get results away against the big boys
IT WAS A THRILL MEETING OUR ZERO
Last-gasp tackles and headers galore but Trusty insists he loved Hoops' backs-to-the-wall display that earned vital point
ONE MAN AND HIS GOG
Tour with Tynie kitman shows boss Neil scale of task ahead
SLOT STERNUL
Nunez strike makes it 9 out of 9 for Pool
UNAITED FRONT
McGinn: Villa feed off driven Emery
THE RAG AND THRONE MAN
ANDERS HOLCH POVLSEN may carry a name that sounds more like a game changer on the pitch than off it.
TYSON BABY LOSS AGONY
| Fighter's wife suffered miscarriage ahead of Usyk bout
HAZEL'S BAFTA AWARD JOY
Sports broadcaster to receive prestigious gong
Hospital infection mum Gail''suffered too much'
A WOMAN who died after she contracted an infection linked to pigeon droppings \"suffered too much\", her daughter has told the Scottish Hospitals Inquiry.
BRAVE RILEY'S TUMOUR FIGHT
Routine pre-school exam revealed golf ball-sized lump behind his eye