O'Neill said: "I'm very cautious about signing players from the Euro Championships or from a World Cup because it's a very different environment. Having said that, I did it a few years ago at Celtic. I signed a lad called Joos Valgaeren who was playing for Belgium at the time and impressed me.
"That said, there shouldn't be too many players on show in the Euros that we don't already know about.
"Virtually all of them play in European leagues and we know all about them. It's not like a World Cup where you might see players from Africa or Asia who you might not have been aware of before."