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.
John is indolent. (not particularly common)
John is a do-nothing. (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.