I have finished my master's thesis and graduated from the university in which I used to study for my masters degree. Now I have two or three months free time and I am searching for a PhD position; in this period of time I want to work on research topic, I see two professors at that university, whose research fields are really interesting to me. Their research field is really near to that of my master's thesis advisor.
Is it considered impoliteness to my master's thesis advisor if I ask another professor in his department (with similar research field to him) to help me work on a research topic?