Apple tree problem - please help.

[pizzaHeart]

Noticed that our apple tree (M26 Christmas pippin, 3 years since planted) got dark brown just above the ground. The bark cracks and peels off a bit. Can anybody suggest what this likely is? A photo is uploading

Muntjac damage

Deer or rabbit! If the bark has been taken off all the way around, the tree might not survive.

@Ilovemyshed @moggerhanger
The tree is surrounded by a net (taken away just to take the photo). The tree is in fully enclosed garden in a city suburb, no deers for many miles. The brown part is mostly smooth, no teeth marks or similar.
Google search suggested that it might be Collar Rot and the tree needs to be removed. But I can’t make such a serious decision based just on Google.
I’m devastated - its apples were really nice 😢

It seems that the graft is failing. Looks like a pathogen called phytopthora to me and I just googled collar rot, and that's what it can be caused by. Collar rot appears to affect mainly cox apples and your pippin is a modern variety.

You could always try to get some air layers to take from branches higher up. It is just about the right time of year to do that, so look up how to do it online and give it a go. You have nothing to lose.

@Yamadori thank you, will have a look