Nwaneri and young Gunners teammate Myles Lewis-Skelly are both expected to be named by Tuchel for this month's World Cup qualifiers against Albania and Latvia.
But Keown said on TNT Sports: "There’s a chance (Nwaneri) may make the international team. That’s a concern, that’s a worry.
"You take it if it comes but if it doesn’t, then he gets a nice bit of time with the manager, resting up between games so there’s a balance.
"It does one thing for confidence but another for the body. When you’re 17, you’re not even fully developed in terms of your cardiovascular system. You’re not really a man yet.
"There’s still some growing to do, and recently he has looked tired, like he was blowing, and this is normal for a 17-year-old kid.
"So it might be a time where he needs resting. And if he doesn’t make the full squad, does he need to be involved in the U21s?
"This has got to be sensibly managed between now and the end of the season."
On Lewis-Skelly, Keown also said: "He’s had some issues, but in terms of physicality, he’s ready to go.
"He looks like he could play and there’s a problem at left-back for England.
"He’s different, more developed. I wouldn’t say he’s a freak of nature, but when you see the strength in him, he is all about power.
"So he is not going to want to be denied the opportunity to play for England."