Depends. Some schools of thought recommend it, the key being you work so hard that it takes a week or more to recover. If you've never made contact with the concrete in your own city, going from car to parking garage to desk and back, then training legs once a week probably isn't enough. If you're climbing ladders with 50lb packs of shingles, then one good heavy leg day a week is fine.
Anything is better than nothing, but up to a point in a parabolic relationship (rather than infinitely linear) more is better. I don't recommend thinking in a 7 day week. Take a bit of a Latin Square by thinking 2-3 days on, 1-2 off if you have the time and work your way up to that energy level. That might look like push day, pull day, legs and abs day. off, off, yoga and abs, pull day, legs, off, push day; and on and on.
If you only have one day a week to workout, the key is to do really heavy compound exercises. What do they call it, the holy trinity; squats, dead lift and bench press, I believe.