The Italian had said earlier in the week that Dunne would be returning to the heart of the defence for the first time in a competitive fixture since the Euro 2012 finals.
But he sprang something of a surprise when he went for Wigan winger McClean, who was discarded by Sunderland in the summer, as the replacement for the injured Aiden McGeady, rather than Anthony Pilkington or Simon Cox.
Trapattoni pointed towards McLean's performance in the corresponding fixture in Stockholm back in March, a 0-0 draw.
"He played well," said the manager. "He is also physically strong and this game is a tough game. It will be technical, but also a physical game against Sweden. They are strong physically.
"At first, I thought about playing with four strikers, but then I thought three strikers is already enough, and because also, during the game, the other options could be very important.
"During the game, I can also choose to have other tactical opportunities. That is the reason."
Dunne back in the fold
Dunne was only able to play 25 minutes of football last season due to injury but he has been playing for QPR in the Championship this season.
And Trapattoni added: "I said at the last conference, I have to think very well about Richard because firstly, it was a long injury, and secondly, he was without a club.
"I said also I would follow him because his fitness would be important. I have seen him play very well in games and, for me, he is the same Richard as he was before the injury."
Captain Robbie Keane said of Dunne: "He's a massive presence. He's my mate and I know how frustrating it has been for him to be out since the Euros, basically.
"I know how excited he is now to be back in the fold and he is desperate to play in a competitive game.
"He's had a good start to his new team with QPR, so he feels fit and he feels sharp. He's a massive, massive player for us."
Rep. Ireland v Sweden is live on Sky Sports 2HD at 7.30pm