Sci-fi short story, i read it in late 90-s early 2000-s. I think it was published in "Tekhnika Molodezhi" ("Technology for the Youth") magazine, but i also think it was translated into Russian from some other language. It's about some guy (engeneer? security?) who investigated disappearence of mining robots and was trapped in one of them. Robot was remotly hacked by unknown aliens and drived into some sort of arena to fight other robot. Robot had basic a.i. so it fought for itself and in the end the guy was able to switch it to manual control and destroy alien robot with mining laser. After that, the guy opened cockpit and ran away, regretting he hadn't switched robot back to a.i. control, dooming it for destruction.
Yesterday, I stumbled upon a link to almost full archive of the "Tekhnika Molodezhi" and through bruteforce searching i was able to find story in question. It's "Zvezdniy gladiator" ("Star gladiator") by Alexey Tsvetkov, "Tekhnika Molodezhi" #12, 1991.