The patient may develop neuropraxia of the brachial plexus or radial nerve
Scalene muscles(anterior & middle fibers) can entrap the lower trunk of the brachial plexus, causing neuropraxia of ulnar nerve
Foot drop is caused because there is disruption in signalling of the nerve to the muscle. The muscle that brings the foot up fails and so the foot drops The nerve can be temporarily injured = neuropraxia and therefore will recover. More extensive injuries to the nerve may or may not recover. A complete transection of the nerve is unlikely to recover without surgery So it depends on the cause and how extensive the injury to the nerve is