Is it acceptable to put "at least" at the end of the sentence without a comma?

When I am using at least at the end of the sentence, is a comma required as below?

I was trying to practice my skills, at least.

Or is it fine without a comma?

I was trying to practice my skills at least.

Just so you know, I don't think it is a colloquial usage. But if it is, please tell me, so that I will not make any mistake of using this sentence in formal writing. Thank you.

The answer will depend on what function "at least" has in your sentence. Is it a parenthetical? You can tell if it makes little difference to the sense of the sentence. I'd say that was the case with your practice:

I was trying to practice my skills, at least.

But consider the following:

She was trying to preserve her dignity at least.

Without the "at least," perhaps she has other things to save. With "at least," she has nothing else left. This means that the phrase isn't an aside and as an integral part of the meaning of the sentence ought not be separated from the rest of its sentence.

But these things are a matter of style.