The defender was named in Sven Goran Eriksson's 23-man squad for this summer's championships in Portugal on Monday.
"It's a fantastic opportunity but I have to be realistic and say I don't expect to start," said the 23-year-old.
"But anything can happen and I have to show the manager I'm ready to play if I'm called upon. I'll be working hard in training because I've also got a chance to prove myself in terms of future squads.
"It can only help my development if I get the chance to play against that kind of opposition. You can't get better than that. It would be a big test for me and it can't hurt for the rest of my career.
"That's how I feel about it. You've got to enjoy being part of a tournament like this but I also want to show people what I can do."
Ledley King wants to enjoy the experience of Euro 2004 - but knows he has to be ready if he gets his chance.