If the liner inside the fridge has a crack forming on the back panel then im afraid theres nothing you can do as it cannot be repaired.
What we do is use silicon sealent and smooth this over the crack and into the crack as this usually stops it from cracking more. But you need to use food safe sealent with it i being inside the fridge. You can still get food safe sealent easy from local diy shops so just make sure its food safe seleant and smear it over the crack and it will seal it in.
It wont effect the working what so ever when this happens so dont worry about that.
If you need anymore info just get back to me.