The Magpies were beaten 4-2 away from home by London side Brentford in the Premier League.
As the Bees maintained their outstanding home form, Guimaraes and his teammates could not keep pace with the top teams.
"Very disappointing," Bruno told TNT Sports Mexico.
"It was a game I was looking forward to after the game against Liverpool at home. I was ready for the game.
"Unfortunately, in the second half, we were not good enough and gave the ball away many times. It was not good enough and I'm very sad and very disappointed for our fans. We have to play for them and today we were not at our best levels.
"I think I can do better. I have been good in some games and others not so good, and I have to find a consistency like the whole team. Everyone can play better in our side."
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