I think he should just go out and take it really easy.
I've run around the outer periphery of Brockwell Park and I'd say that is too far- find a nice circular path inside the park and just run gently round that.
The aim would be to complete it with no pain, and then extend it slightly.
I went out and tried to run far too far, too fast, when I started running.
This is what I'm currently doing. I'm also resisting the urge to take my garmin or watch as at the moment I really don't need the data. I'm just viewing this as getting healthier without pushing myself.