Nerves, pressure, the responsibility not to disappoint: all of it will show. The last time Aberdeen played in a cup final Stevie May was seven years old. That's a lot of years, a lot of letdowns, a lot of supporters disappointed time and time again.
McDonald's in the heart of St Johnstone's midfield these days but he knows what it is like to have the Aberdeen support on his back. He signed in 2008 and had two seasons under Jimmy Calderwood and then Mark McGhee before being released. The cup form while he was there was as grim as ever: they did not even make it to a semi-final in those seasons, let alone a final. Push him on the lowest result and McDonald recalls going out of the Scottish Cup to Raith Rovers in 2010. Raith were in the first division and the game was at Pittodrie.
St Johnstone have lost their last four semi-finals and Aberdeen their last five. "I think it will play on the Aberdeen players' minds more than it's going to play on ours," said McDonald. "Having been at Aberdeen I know what the expectations will be like up there going into the game. They are obviously favourites for the match. Hopefully, that does turn into a negative for them, from our point of view.
"I am surprised it's so long since they won anything. Given the resources they have, compared to other clubs in the league, you would think they would have won more trophies. But for whatever reason, it's just not happened for them. They will be looking to Saturday as an opportunity to get to a final and redeem that. From our point of view, it's a game that we feel, if we play the way we know we can, we are capable of winning.
"I never quite got as far as a semi-final when I was at Aberdeen. The cup runs just never materialised for us, which has been the case for the last few years at Aberdeen. We had a bad cup result when we lost at home to Raith Rovers. It was one we were expected to win and then go on in the competition. You could feel the expectation in the area. It grows and the local press build things up. As a player you are aware of it.
"The best Aberdeen memory for me was in my first season, when we finished fourth on the last game of the season and got into Europe. We had to beat Hibs to qualify and we did. But that was also the day that Jimmy Calderwood left as manager. Straight after the match he announced he was going. It was a strange day because of that. It was a good way to finish the season on the park but then the news about Jimmy put a damper on it a bit."
St Johnstone have been playing the "underdogs" card pretty heavily this week. Aberdeen have already lost three times this season to teams below St Johnstone in the league, and the teams drew when they first met in Perth in August. Listen to anyone from St Johnstone right now, though, and they would have you believe Aberdeen are runaway favourites.
"We knew when the draw was made that their fans would outnumber ours," said McDonald (Tynecastle will have around 12,000 Aberdeen fans and only 3000 St Johnstone on Saturday). "On paper they are favourites but I think being underdogs can work in our favour.
"It is a good position to be in. We are quietly confident that we are capable of getting the right result. I am also sure, though, that the Aberdeen players will be saying the same thing. It is a semi-final so it's a one-off game and what matters is what happens on the day. It will come down to who wants it the most."
The final could be won or lost in midfield: McDonald, Chris Millar and Paddy Cregg against Willo Flood, Barry Robson, and Peter Pawlett. "The midfield always is a key area and that will be the case on Saturday. I am sure it will be a bit frantic in the early part of the game. Once it settles down both teams will try to get our foot on the ball and attempt to play passes and dictate play. We just have to ensure that it is St Johnstone that come out on top."