graduate school - Should I tell the instructor that I will miss the next class?

I have an interview scheduled at the same time as a class, and I'm wondering if I should tell the professor in advance that I won't be attending class that day. The class is important to me, but the interview is more important.

My performance in this subject is really bad, and I'm afraid that asking for an excuse will give the professor a worse impression of me.

Also, the class contains only 11 students.