O’Neill said: “Gabby is enjoying himself and he’s getting a prolonged run in the side.
“If you’d asked him pre-season what he wanted then he would have been delighted with that.
“I’m very pleased with him. But to be called into the England squad – it’s far too early.
“He’s still learning and he’s better off learning his trade with his club.
“I’m not saying this would happen to Gabby, because he’s a down-to-earth lad, but if a young player is suddenly promoted to the England set-up it can affect him.
“He can suddenly think he’s arrived when he still has a long way to go.”