[Daisydog]

We need to first define what "the economy" means. I'll take that to mean the GDP (value of goods and services produced in the country). All else equal, if he works less, then he produces less. This lowers GDP.

What should be done about it? That depends on what our objective is. Is our objective to maximize GDP? Or is it to maximize our happiness? I think most people would say it is to maximize happiness. This may be very much in alignment with maximizing GDP but as we get more wealthy there is probably more of a divergence between maximizing happiness and GDP. So if our goal is to maximize our happiness, then we should do nothing. Presumably he is already doing this. He knows best how to maximize his own happiness, and he has chosen to do that by taking Fridays off.

If we really want to maximize GDP with total disregard for everything else then we probably need to create a stronger incentive for this person to work on Fridays. Right now he is at the point on his utility curve where the marginal happiness (utility) he gets from the money he earns on Friday is less than the marginal happiness he gets from another day of leisure. To maximize GDP we would have to change this to get him to work on Fridays. We would probably need to reduce taxes so the "payoff" he gets from working on Fridays is more than it is currently.

Another possibility we could consider is that we somehow force him to work on Fridays. I'm not going to get into details but I think this will in effect be allocating resources in a way that probably does not maximize GDP. So, I don't think this is a good idea, even from a purely economic perspective.