Tell him to go back to work, and present his doctors certificate clearing him to work there. If they throw him out, they better get ready for an unfair dismissal claimWork has refused to let him go back to work but not officially, just over the phone saying they are discussing it and will let us know.
An employee (full time or part time) has a right to work. No employer can stop you from coming in, unless you are casual or the business closed (redundancy in that case) or some other drastic employer reason.
Go back to work. See if they throw him out, which I doubt they will. Mind you the longer you wait to do this, the more difficult it may be. ie It is nearly looking like you have been forced to quit. (Same as unfair dismissal BTW).
Last point, look up the requirements for his job description. If it says heavy lifting involved (doubtful) then you may need a lawyer