When should he go to the doctor?

Ja
So my SO was working in bed early in the morning a couple days back, still a bit groggy. He misjudged the bedspace and fell on his back. Because he was holding the laptop he fell straight on his back. His back is still quite sore. He says it isn't that bad but I notice him in pain a couple times a day. If there's anyone with some medical knowledge, how long should he wait to see if it doesn't stop hurting and go to the doctor?