The Holland wing-back scored in Saturday's 2-2 draw with Manchester City, a dramatic game which represented another difficult setback for the defending champions.
Willems says he's managed to put extra kilos on his frame with the greater intensity demanded in training at Newcastle. And he admits he can recognise the benefits as he chases a place in Holland's Euro2020 squad.
Asked whether he knew Oranje coach Ronald Koeman was watching him, Willems told Ziggo Sport via Voetbalzone: "As far as I know, I don't know. I just have to keep the focus. It's not that I'm lying awake every day that I'm not there. Then you make yourself crazy."
On his four months in England, Willems is adamant he has improved since arriving on deadline day from Eintracht Frankfurt.
He joked: "Actually, I've become bigger than a while ago - though not in the head!
"I am fitter. The intensity here is much higher than in the Bundesliga, I think."
The defender is on-loan from Eintracht Frankfurt and he Magpies have an option to buy outright for €11.5m. For Willems, he hints he'd welcome the chance to extend his stay on Tyneside.
He added: "I'm not so concerned about it. But if I keep on going, I'll give Newcastle no choice."
- updated December 2