It’s hard to say what is the “appropriate” amount of worry– It is good that this will be assessed by a vet. It is very important that recently neutered/spayed rabbits are in a restricted space to ensure no complications in recovery. While the rabbits may start a fuss, restricting their movement/jumping/running abilities is necessary, just like going through the stress of nail clipping or grooming. You can put a ceiling over the pen to prevent jumping, as well as cover the outside so there are no visual cues to facilitate an urge to escape: https://wabbitwiki.com/wiki/Training_FAQ#My_rabbit_keeps_me_up_by_consistently_chewing_his_cage_bars._How_do_I_make_him_stop.3F  .. A bedsheet nicely clipped, end to end (no gaps or holes peeping through), can provide enough visual cue that most rabbits will not try to jump into it.

It doesn’t look horrible (i.e. probably not an emergency). It probably separated a little bit from him jumping or chewing at it. I would just have the vet take a look as soon as you can. He may need something to keep him from messing with it.