The loss has left Sunderland seven points adrift of safety with seven games left to play.
"We are really disappointed with the result, because we were on top and couldn't get anything positive from the game," Cuellar told the club's official website.
"It's not been one of my best personal years. I didn't play in the beginning and was out for a long time, but I have been working hard to try and get an opportunity and keep playing. But the main thing is the team and trying to stay up."
Sunderland continue their battle for survival on Saturday when they welcome Everton to the Stadium of Light.