McCarthy has been a regular in the squad but has failed to gain the full trust of Trapattoni, who handed him his debut against Uruguay last season but has since played him only once -- late on against Macedonia.
He lost ground on his rivals when he controversially pulled out of the Carling Nations Cup squad last summer and has mostly been an unused substitute since then.
But his recent displays at the heart of Wigan's midfield, particularly in the wins over Manchester United and Arsenal, have caught Tardelli's eye.
"McCarthy we know," he said at a 'Show Racism the Red Card' event at Lansdowne Road. "We know he's a good player and now he grows because he's playing with a bigger personality.
"I think now he is physically very good, very fit and I think whether in the Euros or in the future, he will be a very good player for us. I think he is good at everything on the pitch.
"His personality (has improved). He understands where the ball is. He plays very well and he passes the ball immediately. He is also good physically now."
Tardelli has no concerns over the form of Aiden McGeady, who has been out of the Spartak Moscow team of late. And, while he acknowledged that Kevin Doyle is in a "very sad" situation at Wolves, he thinks the Ireland players at the relegation-threatened club will be okay come the summer.
The Italian is not worried about James McClean's recent dip in form, having watched him at close quarters of late.
"McClean is a new player for us and he's played very well all season," he said.
"I saw his last two matches and it's true that sometimes you can play well and not. With a young player, they can sometimes play two matches well and one match bad."
Trapattoni is in daily contact with Tardelli and has been constantly watching DVDs of his players and of Ireland's group opponents.
"I don't think so. I think it's better to press the Spain team," he said.
"Barcelona is a different team. Spain have different players, they are without (Lionel) Messi, who is very important. I think to play against Barcelona is very difficult. Chelsea played a good match, but I think Barcelona deserved to win."
Tardelli echoed his boss' thoughts when it came to Wes Hoolahan, effectively ruling out a summer appearance but leaving the door open for the in-form Norwich midfielder's return for the World Cup campaign.
And while he acknowledged that Ireland's strength in depth is a good thing for the squad, he says it has made his and Trapattoni's life more difficult as they prepare for the summer.
"Wes Hoolahan is a good player," he said. "Maybe in the future it is possible he will come with us, but now we have many players and we need to decide on the 23. We have 30 players and it's very tough for us to decide on the players.
"The depth is positive -- but for you, not for us, because we need to decide. We have the young players. They grow like James McCarthy, who has played very well this season and also in the last matches. We have James McClean. Everything is possible. We hope the players come to Poland fit."