Chinese Cabbage

I'm growing chinese cabbage for the first time this year. I tried last year but got my seed packets muddled up somehow and ended up with an extra row of kale, must say I did think the seedlings looked a bit iffy

Anyway, I have a few in modules outside with the rest of the brassicas. Question is, are they just as hardy as other brassicas, as they don't look it, but then neither does lettuce? There's frost forecast for the weekend, do I need to put it under cover.

Luckily they're not too far from the cold frame