Ailing Apricot

Ailing Apricot

Observation - Ailing Apricot - UK and Ireland. Description: We put this previously bonny tree outside in May, a little too early so it got a bit cold at night. Since then the leaves have gradually been removed when brown, new buds are there, green wood underneath, the roots look fine, but the tree refuses to grow

We put this previously bonny tree outside in May, a little too early so it got a bit cold at night. Since then the leaves have gradually been removed when brown, new buds are there, green wood underneath, the roots look fine, but the tree refuses to grow a single new green leaf.
Any ideas welcome. Should we plant it in the ground and cover with fleece through the winter? Or bring it back inside? We have fed and watered it all summer to no avail.