The Ireland coach brought on substitute Simon Cox ahead of the Sunderland winger, but justified his selection by admitting that he didn't want to place too much pressure on the young midfielder at the age of 23.
"You can understand how much more tense a young player can be," Trapattoni told reporters.
"It's important we give them the quiet opportunity. Not when we need their performance, under pressure. It's a heavy weight on his shoulders."
Trapattoni explained that he settled on Cox because of his experience with West Brom and his ability to score goals: "I ask you, how many goals did Damien Duff and Aiden McGeady score in qualifying?"
|LEAP OF FAITH?
|22/1||James McClean is 22/1 with Sportingbet to score the first goal when Ireland play Spain.|
The 73-year-old manager, who is the oldest to have ever managed a team at a European Championship, was upbeat about his side's performance against Slaven Bilic's men, admitting that although their opponents were superior, his side were just a little tense.
"We have played good enough, but not as well as Croatia," said Trappatoni. "Maybe we were missing something. Not concentration. But we were just a little bit tense."
The veteran manager also confirmed that he has no new injury concerns ahead of their clash against world and European champions Spain, but did reveal that Richard Dunne, Shay Given and Darren Gibson had all missed training.
"He has blisters, Richard Dunne. He's a little bit tired," Trapattoni continued. "[Given] could play, he is not injured.
"Darron Gibson in shooting, had a little bit of a problem, but he's okay, it's no problem. We have no injuries."