Aleksi Briclot, an artist for Marvel Studios, revealed on his Instagram page an “early exploration for Thor as a gladiator in the arena in Thor Ragnarok.” The design is not at all similar to the end product we saw in the final film.
When Thor enters the arena it is the first time we see him reinvented with a new outfit and a new haircut. It seems like the goal was always to make Thor’s appearance in the arena be different to anything we had seen before and this early design is certainly an attempt at that.
As Aleksi mentions, he has previously posted other iterations which you can see below. What do you think of the designs?