Fred is Scrooge's nephew (his name is not given to the reader until Scrooge observes Fred's family with the Ghost of Christmas Present). Fred serves as a contrast and compliment to Bob Cratchit, Scrooge's clerk; where Cratchit embodies all of the struggles of the lower class, and is comparatively softspoken, Fred is loud, boisterous, and unashamed of his optimism and holiday spirit. He, and the narrator, insist that Fred has the best intentions and does not secretly or openly resent Scrooge's constant belittlings and dismissals of Christmastime "humbug".
While in conversation with Scrooge, Fred tends to refer to him as "Uncle". In private, with his family, Fred has this to say;
“He’s a comical old fellow,” said Scrooge’s nephew, “that’s the truth: and not so pleasant as he might be. However, his offences carry their own punishment, and I have nothing to say against him.”
His family attempt to goad him into saying something a little more pointed, but he politely refuses. Perhaps the only time at which Fred may be said to actually deride Scrooge is during his game of "Yes or No", wherein he is laughing to himself as the family attempts to guess what he is thinking of; we might assume that he is laughing at the idea of Scrooge being described as a dog, bear, ass, etc., all of which are named. Yet, even on this point, Fred expresses remorse for the "fun they've had at his expense", and drinks to Scrooge by way of respect.