Despite his youth, O'Neill admits the Premier League winner is a key influence on his squad.
"His contribution for us has been immense. In the Nations League he was terrific across the six games. Unfortunately we lost him for the games in March," said O'Neill.
"I think he's probably frustrated with his contribution at Liverpool; he'd have contributed a lot more but injury obviously deprived him of that.
"He's a big player with a big future, but he's been unlucky with injuries and hopefully he gets a period without injury where he can really show his potential."
Jonny Evans-type influence
O'Neill also said of Bradley's impact: "Conor has a presence in the squad. As a Premier League winner that will only be enhanced," O'Neill said.
"We've not had that since Jonny Evans. Jonny always had a presence about him and I can see a lot of similarities.
"Although Conor is a younger player, he's developing into that kind of player that Jonny (Evans) was for Northern Ireland."