It seems fear based. Try doing things like giving him his supper just outside the arena doors and then slowly move so that he eats his feed indoors and associates arenas with something positive rather than a breaking in.
On the flip side, he may be trying to avoid work, in that case, get him into the arena and right away send him out on a lunge line. If he's ever to enjoy work, he has to understand that he can't get his way out of it.
Always reward him for going in the arena afterwards while still in the arena so it has a positive impact.
Do you mean he's arena sour? I made the mistake of making my horse arena horse. He was so lazy ! You could barely get him to move. My cure was to take him out on the trails and get him out.