Neck/Pec Pain From Shoulder Press

Howzit guys

A friend of mine injured himself while doing db shoulders presses.

He says that pain runs down the left side of his neck and into his pec.

Anybody have any idea what it could be and how he could rehabilitate it?

Initially he took a week off, came back and lifted at about 50% but he hurt himself again.

Any advise would be appreciated. If you need more info, please let me know and I will ask him to provide me with more information.

Thank you