punctuation - Comma with non-essential expression "in my opinion" at the end of a sentence?

I have learned that a comma is necessary with expressions like "in my opinion" at the beginning of a sentence.

Now, is it also necessary to have a comma in front of a non-essential expression if this expression is positioned at the end of the sentence like in the following example?

1) The novel became more and more tedious, in his opinion.

The only examples I have found so far are front position (comma needed) and mid-position (commas needed as well).