The Doctor's opinion of the Master in "Terror of the Autons" was formed by events that occurred before the episode. Here is the dialogue:
TIME LORD: We Time Lords don't care to be conspicuous. Some of us, that is.
DOCTOR: Look, if you've come down merely to be rude
TIME LORD: I came to warn you. An old acquaintance has arrived on this planet.
DOCTOR: Oh? One of our people?
TIME LORD: The Master.
DOCTOR: That jackanapes! All he ever does is cause trouble.
TIME LORD: He'll certainly try to kill you, Doctor. The tribunal thought that you ought to be made aware of your danger.
DOCTOR: How very kind of them.
TIME LORD: You are incorrigibly meddlesome, Doctor, but we've always felt that your hearts are in the right places. But be careful. The Master has learnt a great deal since you last met him.
DOCTOR: I refuse to be worried by a renegade like the Master. He's a, he's an unimaginative plodder.
http://www.chakoteya.net/DoctorWho/8-1.htm
I noted that when Santa Claus was speaking to the Doctor that the background was white. In the serial "The Mind Robber", the TARDIS was in a dimension that was unknown to the Doctor. This dimension was white, and individuals experienced hallucinations in it. This dimension had a connection to the Land of Fiction. Could the TARDIS have landed in this dimension again?