That means you think if Bellerin has to play we're screwed? I honestly don't see why Bellerin is considered so much worse than Jenkinson was when we got him. Nobody said "If Sagna gets injured we're really screwed" just because Jenkinson had to play.
If you mean we're really screwed because we have to play both Chambers and Bellerin at the same time, that's something else. But as I see it, Bellerin replaces Jenkinson and Chambers replaces Vermaelen, so depth wise, we're no worse off than last year. Probably better actually, since Vermaelen was injured all the time.