However, McCoist insists there will be no room for sentiment when Rangers travel to McDiarmid Park on Saturday - and hopes this will be one game which ends in defeat for the Perth club.
"I'm absolutely delighted for Derek because he was a team-mate and is still a very good friend of mine," said McCoist.
"I'm also delighted for the club he is working for.
"It was more than 30 years ago that I signed for St Johnstone and it's a club that's still in my heart.
"I genuinely still look for their results. It's a great club and I hope they continue to flourish under Derek.
"But we've got to go up there and take the three points and we know how difficult it's going to be.
"We went up there in the cup not so long ago and it was a really difficult game and our goalie had to make a couple of good saves before we managed to get the first goal.
"It's a tough place and you just have to look at their results so far this season.
"Derek has got them playing well and they are really difficult to beat.
"One of the secrets to Derek's side is that they don't really have any superstars and they enjoy working with each other and they enjoy working for the manager.
"When you've got that, you've always got a chance."