/// YEP---It's not affecting just one wheel. You have two three wheel systems. Two front and one rear on one circuit and two front and the other rear on the second circuit. The master cylinder is divided and one half is plumbed to each circuit. One circuit has failed and the brake failure light should have come on. It should have unless the rear caliper is frozen. Then the pressure would be the same in both circuits and the failure light would not come on.

Check you brake fluid when you inspect the brakes. If it is not clear and amber repost. There are other problems that can cause frozen calipers.