There are a couple of difference idiomatic choices depending on what subtext you wish to convey. Here's a selection you can choose from:

If you want to describe someone with *implied criticism* in a single word:

> John is **[work-shy][1]**.
>
> John is **[indolent][2]**. (*not particularly common)*
>
> John is a **[do-nothing][3]**. (*not particularly common).*
>
> John is very **apathetic** towards work.

Or using an idiom:

> John is somewhat of a **nine-to-fiver**.
>
> John does **enough to get by** at work.
>
> John does the **bare minimum** in his job.
>
> John isn't **living up to his own potential** at work.
>
> John is just **scraping by** at work.
>
> John is not **pulling his weight** in his job.

The following may also apply:

> John is very **unmotivated** in his work.
>
> John has **no passion** for his work.
>
> John is fairly **indifferent** towards his work.
>
> John is very **lazy**.

On the other hand, you might want to give John's lifestyle a positive spin:

> John has a **good work life-balance**.


  [1]: https://www.google.com/search?q=define+work-shy
  [2]: https://www.google.com/#q=define+indolent
  [3]: https://www.google.com/#q=define+do-nothing