Leaves look dead but clinging on?

I have an Eleagnus standard tree about 2 metres tall and it’s been growing in a medium sized patio pot. It looked great for the past 2 years but has recently been looking very ill. The leaves have turned from green to yellow brown and it looks as if it’s dying.  In desperation, and with nothing to lose, I have transplanted it during May into a large raised bed with good soil and drainage. Too early to tell if it will improve but in the very high winds this week the brown leaves have remained resolutely on the tree.  How much hope should I have that the tree will recover and any suggestions on things I should do?  Many thanks.