Here are some pictures of what I am talking about.

another picture

one more picture

I am far from an expert, but I'd be worried about this, too.
In my ignorance, but wanting to do the right thing, I'd carefully dig down some and see if this is a deeper problem. That particular root I'd just cut. I'd also water it well after disturbing the roots.

From here I've learned that the hard, brown roots aren't taking any nutrients. It's the fine, white roots that are important.

Anyone can correct me, of course.
I'm going to watch this thread because I have a Pacific Sunset my STBX planted in its burlap, in the wire cage. I'm convinced that's why after 6 years it's not thriving.

You know, I've been thinking about this post a lot.

I am tough on my plants and trees.
If my maples looked like that, I'd water pretty hard.
Then I'd start carefully digging around them.
I'd definitely cut this root.
It looks like the planter didn't spread out the root system at all, plus, all the new, hair-like roots are trying to grow up and over this one. And that circled root looks like it's been growing around, inside a pot for quite some time. I'm willing to bet if you leave it, it'll eventually choke the tree.

What's the condition of the tree itself? Is it thriving? Good leaf condition?

Those pictures just don't look healthy.

He sold you everything but a good job. I think he could of addressed the root system some-what...and wheres the mulch?

wow. looks like it was potted way too long in its container and just plopped in the ground after removal. very good that you caught this... i would carefully excavate around it and cut the sides and vigorously fluff the roots before backfilling... another option is to stick a long knife vertically about an inch from that outside ring and cut outward through the dirt and roots 10 or 12 times, but the former is the best action inmho, and least dangerous to you!