Ibrox side Rangers have progressed to the final of the Scottish Cup.
The Gers got the better of Old Firm rivals Celtic in the semi-finals of the Scottish Cup semi-finals at Hampden Park in Glasgow.
The game finished 2-2 after extra time, and Rangers won the contest 5-4 on penalties.
McKay was among the goalscorers for Mark Warburton’s side and also successfully converted his spot kick during the penalty shootout.
Miller, a former Celtic striker, was impressed with the performance of the 21-year-old winger against Ronny Deila’s side.
“The lads did well and I’ve delighted to be involved with them," Miller told Rangers' official website. "Barrie’s goal was incredible. He’s got that in the locker there’s no doubt about that.
“He’s been fantastic for us all season and he has got better as the season has gone on as well. I thought he was outstanding today.
"Goal aside, I thought he was a real threat for us, a real outlet and a constant thorn in their side.His goal was just rewards for that and maybe the wee bit of luck with the penalty as well.”
During the match, Rangers had 63% of the possession, took nine shots of which three were on target, and earned 10 corners.
Celtic had 37% of the possession, took 33 shots of which 10 were on target, and earned nine corners.
Rangers will take on Hibernian in the final of the Scottish Cup this season.