The Magpies took the lead at the Gtech Community Stadium; however, the Bees bounced back to score three times with Igor Thiago bagging a brace.
Speaking after the game, the England international expressed disappointment at the result, but is hopeful the international break would give Newcastle the edge to bounce back to reckoning.
"Hopefully (the international break) gives us a bit of time to get together after it and work hard and get the details right. We need to hit the ground running after this break,” Barnes told club website.
"It is hard to see what the difference is (between the Premier League results and Champions League). There shouldn't be, really.
"The results shouldn't differ as much as they are. Hopefully, this break gives us time to assess and reset going into the next bunch of games."