Worried about them long-term? Eh, not really. He has a good shooting stroke otherwise (39% on the year from three, 36% for his career). Past that, free throw shooting is mostly a matter of repetitions. I think he needs to put in the work, but I don't see any reason that he can't become a respectable free throw shooter in time.
Worried about them this year? Absolutely. We may see a small amount of positive regression as the season plays out (or not - no guarantee on that), but he probably won't be able to actually fix this until the offseason. So we're going to see him leave points out there for the next several months.