Gareth Southgate's men pride themselves on producing plenty of stars from their renowned academy.
And £4million man O'Neil said: "There's a lot of playing talent out there in the world and, with the pressures on managers to do well, they want to bring in the best.
"The best ones aren't always English. It's up to the likes of myself and the young lads we've got here to keep improving and challenging and maintain our places in the Premier League.
"It was challenging at Portsmouth as you knew you would have people coming in every transfer window.
"You knew you had to perform to stay in the side.
"The initial reaction when the agent told me I'd got to go to Middlesbrough was 'Christ, that's a long way'.
"But as soon as I got here it felt right."